Cessna 172SP. Mfg/Cert after 1998. As you know, there is no MEL for this
aircraft. VFR day flight. Nav/position lights. Say the bulb is out on the
starboard position light.

91.206 says nav/position lights are not mandatory for VFR day flight.

91.213(d) comes into play since there is no official MEL for this aircraft.

Can I fly this aircraft in VFR day flight? Do I need to placard the burned
out bulb?

It's questions like this that kept me out of the better schools... ;-)