Can Reinforce (Street Magic) be used to beef up your worn armor?

It raises the armor rating, but keep in mind, that unlike the armor spell, this would affect the encumbrance value of the armor.

But it doesn't make you glow so if you can deal with the encumbrance, it might be a worthy trade off. Now, anchor the spell such that it reinforces your armor when a successful detect enemies spell triggers it. Then, you can wear normal clothes or light armor and suddenly buff yourself when you need it without having to worry about it.

Not that useful of a spell for most situations (form-fitted or heavier armor in general is a better choice) but in a few narrow applications (places where your clothing is scrutinized, etc) an excellent choice

Actually, the primary purpose was to throw down some freeze foam and then beef it up. I was just thinking of alternate uses.

You can beef up the objects you hide behind. Even good desks are no ballistic shields on their own.

Actually, that's part of the reason for carrying Freeze Foam splash grenades - portable cover

Or just a handy way to catch that leprechaun.

"You bastard, you sufforcated him! Now he can't tell us where he keeps his Lucky Charms!"

Except freeze foam is designed to be porous, to reduce the chances of accidental suffocation! Time to get the Pot'O'Gold!