1) For aRev M1
Open MW2 game folder.
Finde: alterIWnet_configure - change name there
Finde: AlterRevolution_configure - change name here
Finde: aRev.ini - change name here
Not problem if you dont have some of this files, it should work
2)For 4D1 - go to 4d1 website . then go to control panel and change your Username there. Done.
3) For aRev M2 - idk how. Create new account.