Yes. Like for proteins, you can use the CA command. CA actually stands for "Central Atom". The name of this atom defaults to CA, and is stored in _molecule_ca . Change this to "P" or "C1*", or whatever you prefer.

You also have to change the _molecule_ca_mxdist datablock, to approximately 7.5 A. There is a datablock called _molecule_type, which defaults to "PROTEIN". It doesn't do anything, but you can change it to "RNA" if you like.