> Is there a missions.pkt counterpart in Yuri's Revenge? I was using the misssions.pkt in Red Alert 2 (ra2.mix>local.mix) to disable the existing maps.

Don't you have YR yourself?
Try missionmd.ini.

> In order to remove all original maps I set the normal game mode's game type to airwar (or nukewar or siege I guess)
> But unfortunately there are still some leftovers.

> Or are there any means that I can remove the existing maps?

> Thank you :O