Changing defaults for Blog Admins in MultiSite

Folks: On my BuddyPress/MultiSite install I need to change two of the defaults for blog admins:

1), that "Users must be registered and logged in to comment" in Settings/Discussion is set on by default (actually, I'd like it so that the blog admin can't even change this); and

2), that the "Admin Color Scheme" in Users/Your Profile is set the the Blue combination by default, rather than the Gray combination.

Is there some easy way of doing this I don't know about, or a plugin that takes care of this? And if I have to hack the code (I really don't want to, as I'll have to redo the hack with every upgrade), can someone give me an idea of what files this stuff is in? My thanks in advance --