Actually I just looked and its already there, you can put your label in your own resource file and specify it on the custom property like this:
note that the file is actually MyResource.resx but you leave off the extension.
I also looked into the error that you had in the debugger and fixed it. The fix will be in svn trunk by tonight and in the next release. The profile is supposed to let you put a label there and it just displays, using a resource file is not required, just recommended so you can localize your custom work. The problem turned out to be a bug in the SiteLabel control.