use the default node type in the process and add a class to it. See the docs and testcases for this.
If you want to extend it with custom names... that is a completely other issue and not on the list yet to be flexible on that part
But i did it because i've found some undocumented nodes as interleave-start or milestone-node.
What do you mean by adding a class to a node ?
Do you speak about an ActionHandler associated with a Node ?