Ok, found a workaround for new garmin installations. The additional protection is in the garmin-nav file, while the new features such as map switches, present road display etc are enabled through property lists and other files. So when I copy over the garmin-nav file from my usa or WE installation to the SG/MY installation, I'm able to use any unlocked map without renaming it to gmap3d.img and also without losing the additional features. Didn't try for the Thailand one specifically as I'd uninstalled it and the features I need are in the SG/MY installation, but I think it should work just as well.
For those who do not have a usa/we installation already present, here's the file
Download: garmin-nav
Copy it to the Garmin-nav.app directory of your installation after renaming your present executable (just in case there are any issues!). Also set the correct ownerships and permissions, owner-mobile, group-mobile, user-read,write,execute, group-read, execute, world-read,execute
Also here's another mod for the Thailand ipa in 6 parts
Thailand-v2.00.31-(null).part1 - Minus
A tip for having multiple working installations without taking up too much space is to use copy and then link using ifile for large map files etc.