Field status variant

Hi ALL

The GL account in the master data are assigned to field status variant example G004, G001. Currently in the field status variant G004 (Cost Account), the cost center field is optional but i want to change this to mandatory . What are the implication with changing the field status variant(cost center mandatory) after we have been live for 3 years? what happens to all the entries that have been already posted?

Thanks in Advance.

Regards

J