My opponent attacks my unit on abandoned hall, both units have the same might. If I switcharoo my unit and their unit on abandoned hall, does my unit gain +1 might after switcharoo resolves?

Clarification on why it works like that

Yes — your unit gets the +1 Might. Abandoned Hall's trigger ("When a player plays a spell, they may give a unit they control here +1 [M] this turn") doesn't fire until Switcheroo has completely finished resolving; it then goes on the chain and resolves above whatever's left (same timing as FAQ #10497 for Challenge). At that point the ability says "a unit they control here," and Switcheroo only swaps Might values — it does not change control, so your unit is still yours and still at Abandoned Hall. It's the legal choice. Two side notes: since both units have equal Might, the swap itself is effectively a no-op (nothing changes unless a modifier like Shield or a buff is involved), and the trigger is optional and goes on the chain, so your opponent does get a reaction window before the +1 lands. Because it resolves during the showdown, the +1 is in place before combat damage is dealt. It is, because as of now, the "When X play a [card/spell], ..." abilities, where X can be you, a player, etc., care about resolution of the chain item, therefore if you were to counter these, they won't trigger. However keep in mind, that the definition of play will change slightly in Legacy (Set 6), which will then care about finalization and the ability would then trigger, before the resolution of these types of abilities