Can I overstate SEV in comparison to DFMEA in PFMEA?

Generally speaking, SEV values in PFMEA must arise directly from DFMEA. For sure you cannot understate SEV values. The only result of overstating SEV in PFMEA is that during the process analysis the effect for the internal process emerges (e.g. the operator may cut himself/herself), and this kind of effects are not considered by a constructor with regard to DFMEA. Therefore in DFMEA the specific fault may have SEV=4, that is insignificant effects for the user, but in the process (PFMEA) cause the operator to cut himself/herself, that is SEV=10.