Setting specific checkout change (build.vcs.number) for custom build in TeamCity with Perforce

Question

When doing a TeamCity personal build from Perforce, is there any way to set a specific change number to checkout?
I suppose it means overriding the build.vcs.number.* variable, but I found no way to do this - and I don't see the "Changes" tab in the builds' dialog.
I'm using the VS integration, i.e. "Remote Run (Local Changes)" command and the build often ends up broken when someone submits a conflicting update before it starts.