Just a quick question (new player, here).

If I activate Han, then resolve his die in a later turn, and THEN play the Smugglers Run event card which lets me "Activate a Yellow Character", does that mean I can activate him again? or is each character only activated once each round with no exception?

Thanks in advance.

Only cards that are "ready" (facing upright) can be activated. Whenever you activate a card, you turn it 90 degrees to show that it's "exhausted". Once a card is exhausted, it can't be activated again until it's readied, either in the upkeep phase, or by a card like Admiral that can re-ready an exhausted character or vehicle.