I don't see any problem with this at all, sine it's a much better solution than making yet one more prestige class, IMHO. From my owne house rules document:
Fast sneak (ex): When using Move Silently and Hide, the you can move at his normal speed without suffering a penalty to those skills, and only suffer a -10 penalty for running or -5 for quickly dashing to a hiding place (see PHB 69).
Lightning strike (ex): Whenever an opponent you threaten is denied their Dexterity bonus against you, you may make an immediate additional attack of opportunity, which is a sneak attack unless the creature is not vulnerable to your sneak attacks. Even if you have combat reflexes you may only do this once per round for any single target.
Slight of hand (ex): You may pick pocket any object you can hold in one hand easily (your size or smaller), with no penalty due to the size of the object. You could draw a fighters sword before he could, in some cases, and usually without him noticing...
Faceless (ex): In an urban environment with ten or more people about you can hide in plain sight by simply blending into the crowd, even if being watched. People have a hard time remembering your face, so any disguise penalties you may incur through someone’s familiarity with you (such as having wanted posters plastered across the city, or having run in with a certain town guard before) are negated.
Improved feint (ex): You may feint an opponent (see PHB 64) as a move equivalent action, rather than a standard action.
Ambush (ex): During a surprise round you are not limited to taking only a partial action.
Thorn in their side (ex): If others are flanking a target you gain the benefits of flanking against that target, even when you are not yourself flanking. This only applies to melee attacks.