Schema changes will get modified across in the same way as anything else. If you have to have users off one system to make the changes, you need them off both systems. If you can make the changes live, then you're good to go.
"The credit belongs to the man who is actually in the arena, whose face is marred by dust and sweat and blood"
- Theodore Roosevelt
Author of:
SQL Server Execution Plans
SQL Server Query Performance Tuning