lol, nice.
From the ground up, it honestly depends a lot on the style and skill of the hypnotist, and on Mr. Trump himself. A lot of the files you can find are really just porn, with practically zero chance of actually helping anyone into trance. Even for good files, a given hypnotist's style might click with Mr. Trump or not. Trump himself might also have difficulty accepting certain suggestions–maybe he's good with really tactile stuff but bad at visualizing scenarios, then files that lean into or away from that will be better or worse for him. There's also the possibility he just gets bored of a file and wanders away from it over time; it definitely won't have an effect, then.
Anyway, preliminary stuff out of the way, it's given he's regularly listening to a file he's engaged with and responds to, then we can expect that the trigger or behavior suggested by the file will increase in strength over time. Say, after a few weeks snapping makes Mr. Trump feel fuzzy, warm, and distant, after a few months it makes him gently sink into a trance, and after the full year it's a sudden lights out. That's what we should expect, anyway, maybe it takes more or less time based on Trump's predispositions, the hypnotist's skill, etc.
Number 2 is more in the weeds, you probably want to talk to someone who studies psychology (I sure don't). Anyway, the common refrain is that hypnosis can't make you do anything you don't want to do. There is some wiggle room to that, though. Say Mr. Trump isn't in to no goddamn sissy stuff, but super into obedience. Then, the hypnotist could probably still get him to wear frilly panties under his suit, even though he normally wouldn't be into that. In your example, it probably wouldn't work perfectly. Trump is only there listening because he gets something out of it, right? He gets that pleasure a priori. The hypnotist can accentuate that pleasure, and probably reduce it the same way, but it's always going to be something he gets out of that kind of submission. The effectiveness of a suggestion also tends to decay if you don't listen again. My guess is it will depend a lot of the situation. If she gave him something to replace it with ("I wan't you to stop listening to my files because I started submitting to this other mistress and I want you to listen to her files instead." for instance) that might stick. Otherwise, Trump would probably just ignore that one file and continue listening to the others. Probably not really going to be able to tell without a specific scenario, though. I guess the bottom line is that hypnosis isn't magic, so the level of control ironically depends on what Mr. Trump wants.