Hello.
I was wondering, how bad of an idea would it be to add slackware 12.2 repositories to gslapt and telling it to update everything?
and if it's not such a horrible idea that will mess everything up, how about slack 13.1 that works on .TXZ?
I know that vectors package manager won't work with TXZ but how about if I update it to slacks version?

Unless you enjoy re-installing, I wouldn't. While Vector is largely Slackware compatible, changing versions is not a good idea. You will end up with a large number of broken packages. Fixing the problem would be a nightmare.
Paul.