will it hold its tweaked shape over time? or will it need to be adjusted here and there?

It may need adjusting if it's on the very fine edge of being too open or too closed. There is quite a bit of margin in the middle to where it will never need to be readjusted. If it is too wide, it won't slip back under the sear and you won't get a reset. If it's too narrow, it will never release the sear or it may release it only when you put a little tension on the slide. In either case, if you adjust it to where it works reliably, there should be no need to touch it again.

The issue isn't adjusting the loop for its interaction sear - the problems arise with the trigger reset - there is a VERY narrow window where you will get the sear where you want it and lose your reset. Think about this adjustment and make sure you won't mind sending you gun to S&W for work not covered under the warranty. I talked to 3 different folks at S&W CS before deciding to leave well enough alone. You don't mention why you want to tweak the loop.
Good luck!

I adjusted my loop according to the Apex video. No readjustment needed in a year of casual shooting.