Really, no-one could recognise you if you wore a closed helm?

I would like a perk that lets a thief hide small blades on their body so that the guards don't confiscate them (useful for important meetings and prison escapes).

This kinda of game mechanic, while cool, has not place in the Elder Scrolls. At least not in the capacity most people would want it to be. To have this feature in the game just because you want to commit crimes and get away with them would unbalance the game too much. In NV the game revolved around the main factions and thus the disguises had actually reason and usefulness in the games plot and game world. Skyrim's main story line and game world couldn't support the reasoning behind the inclusion of such a feature. However if the Nocturnals Cowl is back, and with its stats untouched, then you could have something to fulfill your wish of crimes without penalty. In Oblivion, Nocturnals Cowl allowed players to commit crime as the Gray Fox and the infamy and bounties incurred would not affect the players normal crime stats.

Oh my! You sir are my best friend now. That made me laugh so hard. :rofl: I commend you