Overall or barrel length is irrelevant as it's a rimfire. It only needs to have a fixed stock in order to be reclassified as NR.
See FRN#145651-17 for example. It's a Vz61 .22LR converted to a fixed stock the RCMP deems "permanent", and therefore reclassified as NR. Not sure if the owner is here but he mentioned it a couple months back on Reddit.
I'm sure if you inquire the CFP about FRN#145651-17 they can provide you guidance on how to follow this conversion.