As someone who has put over 2k hours into the tools, here's my concerns.
It's easy to set a weapon to not auto setup, but not as an ability toggle; the flag isn't directly editable to my knowledge. My first thought in regards to how to accomplish this would be a literal weapon swap similar to Sherman shell swap, which may have unintended side effects like animation issues.
Yeah because first this was mentioned to the bug fixing team and it was discussed that the HMG is working as intended for buildings. However I could see if the mods could actually make this change work it would be an appreciated change. What you just mentioned makes the situation with it sound a bit complicated to make work though
Are you selecting the MG and right clicking or using the "get out of garrison" button ?
I have certainly made that mistake in the past. Now I try to be very careful when maneuvering my HMGs in and out of garrisons