When Switcheroo swaps current Might values between two units, does the Forbidding Waste penalty get counted once in the swap calculation, or does it apply separately on top of the swapped values?

Counted once — the −2 is part of the unit's current Might when Switcheroo resolves, and it then keeps applying as an ongoing static effect rather than being added a second time.

Switcheroo determines the difference between the two units' current Might (Rule 433.1.b), so Forbidding Waste's −2 is already baked into that number and the swap modifier is sized to hit the correct totals. Unlike a spell effect, Forbidding Waste is a passive "while" ability, so it doesn't snapshot — it re-evaluates continuously (Rule 477.3.b, FAQ #10921).

Practical result: after the swap the unit at Forbidding Waste still has the −2 applied on top of the fixed swap modifier. Example — lone defender base 4 (currently 2 with the penalty) swaps with a 6 Might unit: the defender ends at 4 − 2 + 4 = 6 and the other unit at 2. If that defender later stops being alone, the −2 vanishes and it jumps to 8, while the swap modifier stays fixed for the turn.