This works!!! Thank you so much!!
If you want Mp3tag to change the modification time of your files every time you change something in your fields, leave it UNTICKED/DISABLED (as shown in screenshot).
This way, external software can use this changed date to decide what to do ("backup", "update"...).
If you don't want Mp3tag to change this date and time, ENABLE/CHECK this setting and preserve the modification time = keep it unchanged even if you change something inside the file.
If you are still interested to solve this part of the problem, please open a new thread.
Then we can start from scratch with your import and CSV - now that you know how to refresh metadata in MusicBee and show such external changes.
Also in practice.
And this hint to handle a 3rd party program could already be seen 55 posts ago:
@mattiebear I do believe the efforts that several people have made over the past two days could have been reduced significantly if the original suggestions had been applied. @ohrenkino @LyricsLover @poster and I all suggested at various times from the beginning that you needed to refresh the MusicBee library to capture any changes made externally, i.e using mp3tag.
Bottom line - virtually ALL players use an INTERNAL library for managing their data. If for whatever reason you are managing metadata for your music files externally, these music players almost ALWAYS neeed to have this library forced to refresh. Some make this process easier than others. Please be aware of how to do this with your personal player of choice. This is not a function of mp3tag!
I want to acknowledge that I wasn't able to follow the instructions provided by certain users, but I think it's important to highlight why. The tone in which the guidance was provided came across as patronizing and condescending, which made it harder for me to engage and learn from. If the advice had been offered with more respect and patience, I believe I could have resolved this issue much more quickly. It's interesting that after specifically stating I did not want to engage with a specific user, instead of respecting this, they decided to ignore me and continue to comment, resulting in a 'told you so' post at the end.
But this isnāt about pointing fingersāit's a reminder that how we communicate matters just as much as what we communicate. I'm sure you're all here to help others, and a bit more empathy and humility can go a long way.
That, my friend, was entirely in your head. You provided few details at first, which meant that you received requests for more info. That was not condescension, but simply a need for details.
You do not control who responds here. Ohrenkino is a senior and vital contributor, and he made an important observation in this thread:
You ignored his suggestion, which was in fact the key to solving your issue. Instead, you proceeded to insult him.
We do not need to be lectured. Responders here are volunteers and their time and experience are valuable. They are not here to hold your hand. If you require more "empathy and humility" then perhaps this forum is not for you.
Oh I agree with you completely!
At this point its entertaining me how upset you're all getting. You carry on lovely. 
I believe it is safe to say this thread has run its course. The solution for the original request has been provided.