Hi Brian,
Yes. On the Client-Side tab of the button make sure you refresh the field holding the path, just the comment will do since that's what you want to change.
Now, on the field itself put something like the following in the comment: choose(p_web.gsv('path_exists'),'OK','Please create'). This should do the trick (assuming you have a session value holding information about whether the path exists or not).
Peter