If +1 from rumble scrapper arithmetic and re-evaluate so if it gets switcheroo how to rezolve?

Rumble's +1 doesn't get added again after the swap — Switcheroo already counted it when it snapshotted both units' current Might, and its ± modifier is fixed for the turn.

So it doesn't "re-evaluate" the swap; the layers just sit side by side. A 4-Might Mech under Rumble (5 current) swapped with a 3-Might unit ends at 4 + 1 − 2 = 3, and the other unit at 3 + 2 = 5. If Rumble leaves (or a second one enters) after the swap, layers re-evaluate and the bonus updates — but the Switcheroo modifier itself never recalculates (Rules 433.1.b, 477.3).