Yikes! Don't even say that!
It's okay to put a longer barrel on it, but a full length stock makes it an SBR, which is Class 3! You gotta pay the $200 and get the tax stamp BEFORE you purchase a full-length stock...unless, of course, you already have a 10/22 rifle, in which case you can legally possess an aftermarket stock...
I know you were cracking wise...but this is actually a minefield waiting for the uninitiated...
Michael B