May I just add: Yes it is drastic, but it is the only way to stop people from seeing it*, because there is no function to stop sending such information as the psm. You either send it to them, or you don't have a psm =p
Also, I'm thinking, in order for them not see the psm, you would need to block the group before you changed your psm. Else it would probably be updated on their contact list before you blocked them, thus defeating the whole objective
* and by 'seeing it' I mean, it'll just stick to the previous psm on their contact list. - Until you unblock them.
Someone correct me if I'm wrong, please.