ENCODINGTIME, RELEASETIME, and CREATION_TIME are very different because, on MediaInfo.exe, CREATION_TIME, for mkv files, is shown as "Encoded date" while ENCODINGTIME and RELEASETIME are shown under their own fields via MediaInfo. Furthermore, CREATION_TIME, when used upon mp4 files, using ffmpeg's "-map_metadata 0", will push the entry date in the CREATION_TIME field from Mp3tag, and will reflect Windows File Properties DETAILS tab "Media Created" tag. You may see it as a waste of time, but it's actually essential. For example, I am in the medical field: we read studies to formulate new plans on how to better treat and assess our patients. If you go onto PubMed, they have a filter regarding "Dates" on the articles, establishing how old the articles or scientific journals are. Asthma guidelines were changed in 2019, and, just like the encoded date, if you don't have that timestamp, you may think the videos (articles) are new, after being remuxed by mkvmerge, which doesn't give you the option of preserving the original encoded date. Regarding Gillmeister Rename Expert, from the two images below, you can see how pivotal the CREATION_TIME (aka Encoded Date) plays a role in assigning a TimeStamp to reflect on Windows File Properties GENERAL tab. Moreover, looking back at the "Encoded date" image in my previous response, I implemented the CREATION_TIME as 2019-12-25T17:18:52Z, and since I remuxed it with mkvmerge, under Encoded date, it displayed it as 2022-01-16 22:13:16 / 2019-12-25T17:18:52Z. Afterwards, I use mkvpropedit, via Mp3Tag Tools, to writing the MP3Tag CREATION_TIME entry into mkvpropedit, producing an Encoded date as 2019-12-25 17:18:52 / 2019-12-25T17:18:52Z, and then I ran Gillmeister rename expert, as you can see from the images below.
I know that I may sound like a broken record, but I like my videos to be organized regarding when it was encoded, and @ryerman, with his VBS Script, helped me return the original Encoded date using mkvpropedit via the Mp3tag's EXPORT options. Thus, I am aware that @ryerman stated that I shouldn't post anything, under Support, that's not specific to Mp3tag software, but my request was Mp3tag-related: regular expression to convert between timezones. Nonetheless, thank you all for everything, especially @ryerman: I truly appreciate the patience and how you assisted me on all my request.
P.S. Sorry, I wouldn't be wasting any of your time if MKVToolNix (mkvmerge.exe; mkvpropedit.exe) had an option to preserve the original encoded date, or if I could create a batch script that would easily allow me to write ample differing CREATION_TIME via mkvpropedit GUI.