My post above is about as informative as I care to get about the
subject. You can play a thief and see what you can do and cannot do,
or you can ask a thief in game. Generally speaking, however, if you
fully complete one path, you'll be able to dabble in other areas.
How much you are able to dabble depends on the strength of the path
you finished, and the strength of the skills you are dabbling with.
I've now met my dabble quota for my lifetime.