You are using the pccc decoder in an incorrect way.
Please see attached corrected grc file:
there are two ways to use the pccc decoder
(i) either as a combo or (ii) in conjuction with trellis metrics.
I have provided in your file both ways.
Regarding you second question about whether you can define your own FSM:
Of course you can! This is the whole idea of the FSM class!
Please read the extensive documentation on how to do that in:
(or wherever you have your documentation installed),
and let us know if there is something you do not understand.