Business Rules - when a company changes hands

We have a site which is currently owned by Company A and has a business rule which recognises email from company A and the rule auto-completes the fields.

Company B (who we also support) has purchased this A site and it will now become a B site.

I can see how we remove Business Rule A, but how can we associate the B rule to this site please?

Also, as a wishlist item, can the default for the top field "Helpdesk - Business Rules for:" please have a tick box for Default Settings as it took us ages to work out how to add a new rule that didn't only affect the last site that was cached (or from the look up).

Thanks in advance.