(imported comment written by BenKus)
I think this is a good point… I think this change to a non-editable field was made a while back when we had a few customers cause damage to their databases when they used only partially privileged accounts to do admin activities and in at least one case, they suffered serious problems as a result.
We did add an override in the registry which sounds like it will solve your issue for the moment:
You can use this:
If non-0, user can type in the database username they wish to use instead of ‘sa’
Note that you will need an account with full privileges on the database to set up the system and make new users… So if it is not the sa account, it should have the same permissions as sa.
Perhaps it is time for us to revisit the decision that made us make this change in the first place.