Please support proxy users. They allow people to impersonate another user which is useful for all kinds of purposes regarding security and auditing.
So, I got this user called MyUserName which can act as a proxy user for OurSchema. To log in, I use MyUserName[OurSchema] as the username (and my own password). Then I can make modifications to OurSchema and basically work as if I'm logged in as OurSchema.
This works well in any tool. In Schema Compare it almost works, but there seems to be an issue with the grants. The grants are not detected, so when I run SC with a proxy user, I suddenly get about 3000 differences.