Incase you do not wish to give access to user to update IT0003 then you would have to execute the dynamic action in the background itself. So the /D in the second statement should stay there. Exactly which date from IT0377 do you want to be set as earl pers RA date? You can directly assign that field to PRDAT. You may not require a subroutine.
Debugging would be possible for dynamic action as well. Either set the breakpoint in your subrountine or simple use /h when you start your termination action.