does mel newly awakened when empowered give additional - might when applying switcheroo?

Yes — an Empowered Mel does add the extra -1 [M], applied to the unit on the losing side of the swap.

Swap isn't a single value-setting action: Rule 433.1.a/b says a swap creates two effects — an Increase for the difference on the lower-Might unit and a Decrease of that same amount on the higher-Might unit. That Decrease is a "give -[M]" event to a unit your spell chose (Switcheroo targets both units), so Mel's replacement effect (Rule 370.1) replaces it with a Decrease of one more.

Example: unit A at 5 [M], unit B at 2 [M] at the same battlefield → Switcheroo gives A -3 (Mel makes it -4, so A ends at 1 [M]) and B +3 (B ends at 5 [M]). The swap is therefore no longer a perfect reversal. Only the -[M] side is affected — Mel never touches the Increase.

Edge case: if both units have the same Might, Rule 433.1.c says the swap does nothing, so no -[M] event occurs and Mel adds nothing (same logic as the official Stupefy-on-a-1-[M]-unit ruling, FAQ #11759). This all assumes Mel is Empowered and you control the Switcheroo.