Multistore support

Hello,
2 years ago i installed multistore on 1.5.4 , the multistore has 2 domains and in the beginning i thought the 1st domain that's default store will be the successor but as the time pass the 2nd store had much more success.
problems are when you want to buy or get an extension it most be multistore supported else it will installed only on the 1st default store that is much less popular...
questions are:
1- can i switch between the stores (secondary store to be the default) w/o making a big mess to current data ?
2- how can i install a non multistore ext. but only on the 2nd domain (not the default)
3- if I'll delete my default store will the 2nd store become the default

i really regret that i installed multistore it would be much easier for me to install and managed 2 admins

hope some of you maybe recommended on solution for my issues.

thanks,

any one??