I'll add a variant to the original question :
I paid for a transatlantic economy ticket a couple months back (before getting to 1K) since then I reached 1K and my upgrades to business have cleared (even got a seat assignment) ...

At this point :
1) is there any benefit to call UA to reenter my MP# ? (like having higher status should anything unusual happen , cancel flight/rebook, op-up chance higher ... )
2) are there any risks of loosing my confirmed upgraded seats while doing the reentering the MP# manipulation ? (what do I need to say so that my upgraded seats do not disappear !)

THanks

Pierre