Straight nitriding has essentially no dimensional change.
Don't know about carbo-nitriding. It's midway between nitriding and carburizing w.r.t. the temperatures involved and what it adds to the surface chemistry. A quick check finds some people saying no dimensional change, other people saying some dimensional change. I did find one paper that claims nitro-carburizing produces less dimensional change than carbo-nitriding, apparently there's some.
Consult your heat treater, and they will consult the tea leaves. Or, run a prototype sample and see how the actual part behaves.