Hi Venkat,
In addition to above you may check below one as well.
"In order to have both Billing and Service render date as same, as far as i know, you don't have standard solution, but, you can try using USEREXIT_MOVE_FIELD_TO_VBAK".
or
User exit in program RV60AFZC.
FORM userexit_fill_vbrk_vbrp.
Let see what experts say on this.
Regards, Sai Krishna.