How to update the contract modifier

Hello,

We need the ability to change/update the contract modifier after the contract is saved.   Is this possible?

Our contracts are renewed automatically and the modifier is populated.   But our business needs sometimes to update the modifier to a meaningful information at the time of validating/completing the renewed contract.

Once the contract is saved the modifier is grayed out (read-only). 

The auto-numbering flag "Allow Manual" only applies to the contract number.  

Is there a set up to enable the contract modifier to be update-able?

Thanks in advance,

Ingrid