If it is configured right ...
When you open the drawing in a session connected to Windchill it should get the format from Windchill and ignore the format that is there on the drive. The reason it should do that is that the drawing has the format name in it and the first place it should look for that name is the local Workspace, then Commonspace, and if not found, then the current directory.
If you first opened the format .frm file and saved it to your workspace, Windchill would show a name conflict and would not allow you to check it in because it wasn't checked out. You could Add the Windchill version, which would overwrite the local version, and, not being new anymore, would also not check in.
Finally, the Admin for Windchill should have set the permissions on formats so that no one can change them without an authorized effort.
It's a great question. Maybe the Cliffs Notes guys could work on a guide.