Hello Tammy Koopmans-Lee (TammyKoopmans-Lee)
If you select a project and retain all the KEEP settings nothing changes on that actual project (OK greyed out).
You need to select the changes - e.g.
Add the template you wish to use
The error message is really a warning to tell you that corruption COULD happen when changing the settings.
Although TM's and TB's are rather robust- it is always wise to make regular backups-
We even have apps to help you do this-