Locking entire Form when it has a specific Status Reason

I have a Purchase Order entity which has various Active Status Reasons.  Once it's gone through the prerequisite states, it's Status Reason = Active; so Status = Active and Status Reason = Active.  When that condition exists, I need all of the fields on the form to be locked so the Purchase Order can't be changed; it's now a contractual agreement.  We should be able to Append To it with payments that decrement it's balance, but the user should not be able to change it.

Is there an OOTB way to do that?  I know that when you change the Status to Inactive, it llocks everything down; but I need the Status to remain Active, just locked.

Thanks!