Need to make a mob that is friendly for some, but hostile to others

Hello again everyone,
Just a quick request here...I am wondering if there is a way that I can make it so that after a player does something on the server, i.e. finish a quest/dungeon or just be of a certain race/class, then a certain mob will no longer be hostile to them.

I am thinking of putting a bandit type mob into one of my towns, but for my rogue/stalker type class have them eventually be in the same 'faction' as the bandits so they will not be targeted by them.

Any help would be...

Need to make a mob that is friendly for some, but hostile to others