Of course, the originals will remain in the backup and the newly created files will be stored on a USB 512 GB and will be used for playback only on that player. But I'm still thinking and looking for some less "destructive" and simpler method, because the program in which I would do it does not allow loading all directories at once, but only individual files.
I find it mind-boggling that such a new device fails to properly support flac. I have an mp3player form 2011 that fully supports it.
My take is that the device manufacturer has to fix the flac support if the device lists supporting flac as one of its features. Forcing different tags into flac files might work for you (props for your creativity to try that) but I would also not recommend doing so.
Recompressing these new files with the verify option should tell if forcing id3 tags into flac files changes the music part (I don't think it would).
If it is such an effort, you might want to consider not using the internal player of your internet radio until the device manufacturer fixes flac support and instead use one of its inputs to play music on it from a different source with better support.
A few possible solutions would be to try if your internet radio can be cast to via UPnP, in which case you could select and control the playback on your phone in an app like Symfonium which fully supports flac.
Or if that is not an option you could hook up a raspberry pi to one of the inputs of your radio, install something like upmpdcli on it to then once again cast to that via your phone. Even a pi zero which is very inexpensive suffices to play back high res flac files (I tested it up to 192KHz 24bit).
I'm personally using upmpdcli and symfonium to play music on a raspberry pi 3b with a Hifiberry DAC+ Pro HAT hooked up to an old Denon PMA 1510AE and it works flawlessly with terabytes of music.
If there is interest in choosing this type of internet radio, I can come back later. It was indeed a difficult journey of about 6 weeks, since in this price category the manuals do not even include basic technical data. The sellers could not properly answer my questions, and what is sad, neither did the manufacturers if they answered me at all. Statements about the same thing sometimes differed greatly from each other and were even contradictory.
Given that I don't have my own home network, my basic requirements for the device were, among others: LAN connection (RJ-45), bluetooth Rx/Tx, ability to play flac files from USB, ability to load USB at least 256 GB in size, ability to display on display basic data from ID3Tag - artist, album, track, codec, data stream, album cover, file path, ... . As I already wrote, the device is not able to display these data except for the name of the file being played and, in the case of MP3, the image of the album. For this flac, only the name of the file being played will be displayed.
Thanks for the tip on the Symfonium app, which looks interesting, but neither this nor the others I tried within UPnP/DLNA from an Android mobile phone: BubbleUPnP, MediaMonkey, HiFi Cast work on the device, although the playback starts with a slight delay but after playing 1 song, the connection seems to be disconnected and the playback stops and doesn't continue. Nothing will appear on the display except for the song title. I tried to set various parameters in the app, but the result was the same. I don't know what I'm doing wrong. Interestingly, I also own another older AUNA Harvard device on which everything works perfectly. I assume that the problem is probably in the device itself.
I just remembered, a friend of mine had a streamer that required a Folder.jpg with a capital F - nothing else worked whilst playing from USB. It's indeed a longshot, and perhaps you've tried it already.
Your player seems to support UPnP, but only half-work with those control points - perhaps you could try them with a reputable server like Asset UPnP or Minimserver, if you haven't already.
Also, you could check if there is a dedicated control point for this player from the manufacturer (not that I think there is).
But many streamers implement UPnP/DLNA very badly, so you may be out of luck (or hope for a firmware update).
I tried all possible combinations, cover.jpg, folder.jpg, coverart.jpg, .... and now Folder.jpg. He doesn't work either. I found that the image only needs to be inside the file. I also have a small SanDisk MP3 player and the image is only displayed in it when it is an external file named folder.jpg and the image must have dimensions of the same values and only up to 300x300.
I don't have a home server, so I probably won't be able to use the programs you suggested. For example, I can use KODI with a Sony android TV, but the app must be running and thus blocks watching programs. I can only use the app on my android phone.
I don't know how to find the control point, the manufacturer does not respond. Telestar was bought by Nedis a week after I bought the device. The device is no longer even available on the nedis.de website, so I don't even expect any support or updates from the manufacturer. They haven't even replied to my email yet. I guess I'm unlucky. Bluetooth works as it is, but I assume that only with the SBS codec and so I can forget about the transfer of flac files with a higher data rate. All I have left is the USB.
They install in Windows and Linux, so all you need is a PC.
For example install Asset on the PC, and BubbleUPnP on your phone. Then connect PC + phone + the Imperial to the same network. The control point (BubbleUPnP) should find Asset on the PC.
I also searched a little and found some manuals here and here which mention Soundmate here as control point. I've never used that app, but it seems to be "the official" CP for the Imperial? Seems outdated though, but at least it has a UPnP button... Definitely worth a try if BubbleUPnP doesn't get you the artwork.
Of course I cannot say that you'll get the desired artwork via UPnP (it does look like your unit needs a firmware update). But at least Asset UPnP and BubbleUPnP would be the first apps I would try since they (and a few others) are dedicated to UPnP/DLNA. Kodi, which you mention, and others do a zillion things, which isn't always great.
I really appreciate your effort to help me.
He tried the Soudmate application first. It is primarily intended for Imperial products but has several shortcomings. The application disconnects after a certain time and then it is necessary to "pair" it with the device. When playing from USB, apart from the name of the file being played, the album image and information about the type of codec being played (but without specifying the bitrate, which is then useless information for me), you will not learn anything, just like on the device's display. The biggest drawback of the app is that it is not possible to browse (display) more than "19" directories or files, which is absolute nonsense. I consulted the creators of the app Soudmate team from Hong Kong about these things. They answered me very quickly, saying that if some things are implemented, they will be included in the future version, some in cooperation with the manufacturer. As I wrote, fy was bought by the company Nedis, which in my opinion is just such an e-shop, from which you can probably no longer expect any support.
I can try the procedure you suggested, but I would like to minimize the number of devices running on that phone only.
As I wrote BubbleUPnP, I tried but I could not start more than one song. Yesterday I managed to install an application (I don't know its name anymore, probably Tune...), where the playback was already continuous but there was a very long gap between the songs being played, the device disconnected, a text about the need to connect the mobile phone was displayed and then it connected again and playback continued. It's very distracting. In my opinion, it's not right and it needs to be fixed because, as I already wrote, I don't have such a problem with another device.
It's been a month since I wrote to the manufacturer, but he still hasn't answered me, probably for the reasons I described above. I'm from Slovakia and I don't speak German or English enough to call him and explain my problems. I'm writing through google translator here too, so I apologize if the grammar isn't always quite right.