Because of such go live issues, a date type is used to indicate hire date or start of service date. In V_T559L ->generation rules->accrual tab, use the date type.
The date type in IT 41 can be inserted during hiring personnel action, using dynamic actions. This is a very common config, if you have seen the posts in SCN.
For go-live, LSMW is used to populate IT 41 in bulk