You should be fine going back to your old permissions, since the elevated permissions were only needed to change the DB schema for the new version.

I have to balance the pros and cons of many things in GSP. While I could in theory ask for new login credentials, that would require building a UI to support it, and currently the 2.5 => 2.6 upgrade does not use a UI - it just silently happens in the background. It would take time and delay the release.

As a compromise, I describe in the Admin Guide how the upgrade process requires elevated permissions, and if this affects you, to either provide those permissions before upgrading or modify the connection string in web.config to a different account. I believe this is the appropriate balance.

I do appreciate the suggestion, though.