better off to email slushs than mybitcoin, mybitcoin is gone plenty in the forums about that fiasco already.
Can see an email at the bottom of the home page in the about section on mining.bitcoin.cz
I emailed members of my pool with info on the mybitcoin thing and helped a few change wallet details
pointless contacting my bitcoin (even if you could) they cant change your wallet adress on a pool (unless you gave them your login deets as well)
to change the wallet address on slush's pool (re post heading) contact slush's pool.