I would see it as an opportunity to be attempted; but of course you need to be careful as you've said, and to expect opposition.
The thing with a disguise game is you need two extra things: A following on the inside (People who agree with your cause while NOT being magicaly influenced), and a dupe (Someone to take the fall for you if things get too hot.)
If you have those, and your GM is willing to run this kind of game, it can actually be THE POINT of the campaign to do what you are trying to do.
while amusing, I don't think this is a practical plan (casting Hypnotism with the command "Trust me").
a) trust does not imply others will take action on your behalf. They will say, "I trust you, go and try it and let me know how it works out". What it WILL do is earn you some cash - such as if you suggest they buy a certain brand to cure what ails them etc... a typical con artist/confidence trickster scam.
b) with a permanent duration you are leaving detectable spell traces. Any diviner or enchanter is going to figure out what is going on after they cast Detect Magic. Don't worry - Dispel Magic runs off caster level so it should be easy to dispel.
c) hmm there could be those snarky Atonements to pay for to keep yourself on the PFS playable side of Neutral. Yes, the first one won't cause a ruckus, but the 10th casting? hmmm... Now if you are doing it for their and you benefit - that's different.
d) lastly, once it gets out that your caster is doing this, the Aspis agents will be by later with a press gang to help you join their organization, if the gypsies, thieve's guild, or local constabulary don't get to you first. Minor felonies have their rewards. Remember while the subject doesn't remember what you did, casual observers will.
"Duration 2d4 rounds (D)"
"Even after the spell ends, the creature retains its new attitude toward you, but only with respect to that particular request."
No enduring magic, no detecting, no dispelling. Just a residual psychological effect. Just like the wall of stone that appears when you cast Wall of Stone.
A) "Trust me" is just the opener, not the entire plan. It's just a way to get them to waive their saving throws as you proceed to scrub the rest of their brains.
B)There is no magical trace because it's not a permanent spell. There would be no more trace of it ever having been cast than there would be from a Bull's Strength cast 6 months ago.
The biggest problem I see here is a metagame issue: what are the other players doing while your sorcerer is building a cult?
If the others are on board with doing this, I'd let it work, and start thinking up reasonable (but solvable) problems for your cult to face.
If everyone else at the table would rather head down into a dungeon and kill some orcs, I'd shut this down.
I agree the duration is finite (somehow I got permanent on the brain) so ignore part b).
I understand the group dynamic, and yeah, the other players at your table will be bored. I think this is more of a fantasy inspired by the wording of the Hypnotism spell itself, rather than something "game changing" as it were... lol
I agree that Hypnotism is better than Charm Person in the long run. Less risk and longer impact.
However... while the spell leads you to believe that the person will always trust you forever and ever, it ignores the fact that learning and behavior modification continues to occur after the spell is cast. So the results of the trust you have inspired will continue to require reinforcement to maintain as other events modify that behavior. It is much the same as the aforementioned Wall of Stone. Yes it's permanent if nothing ever changes it, but a guy with a hammer & chisel can reshape it, cut it up, etc. So as the caster of Hypnotism betrays the targets blind trust, the targets will learn and modify their behavior accordingly. So pretty much you are looking at Charisma/Diplomacy checks to keep the attitude from lowering a step towards Unfriendly.
The other perennial issue is the in-game level of technology versus what you know about reality today. The in-game level of technology is generally very basic, you need Technology feat to use your skill ranks on advanced technology. Alchemy leads to Chemistry but is not the same. Similar to a charisma based sorcerer knowing what a brain does much less how it works.