1. alias
^ that launches another mirc using what ever compat mode you set it to., replace $mircexe with what eer executable you want to use.

2. batch code where you state "Type this in the second mIRC when it starts //echo -a $os"
^ that was so in that second mirc from (1) you could see that it was infact in that compatability mode.

and 3. another code that mirc can run
^ this was an alternative method of launching an app using a compatability mode.