PCR change with date effect

Dear Experts,

I need to change a PCR with the retro effect from 2014 July. That mean client is paying OT amount for national holydays double.Already one PCR is wriiten for that. Just giving the total hours of OT in infotype 2010 it will calculate amount and will show the wagetype in RT after running the payroll. But  Now I want to make it tripple from July 2014 with retro effect. I can change the PCR and make it tripple but I want to know how to get the retro effect from July.

thanks in advance.

Anil