I'd recommend you put in the "R" in field 10; but either use a STS or RMK in field 18 such as "RMK/RNP-5" or "STS/RNP-5". There shouldn't be too many APP/ARR controllers offering a C172 an PRNAV STAR without thinking seriously about the status of your nav gear.
Also though, don't file your route to the PRNAV STAR points, file the route to the main aerodrome NAVAID (VOR/NDB etc.), that way automatic systems should not/won't allocate you the STAR automatically; thus it gives us a good chance at our end to spot it.