FAR threshold updates on current contracts

I don't understand the question.  If the purchase order (contract) is already awarded, leave it alone.  Thresholds such as the micro-purchase threshold apply in pre-award situations (before contracts are awarded) to settle on clauses, competition requirements, and so forth -- all of which is water under the bridge once the contract is awarded.  Leave it alone, and enforce it as it is written and as it was agreed to.