Can I play Smoke and Mirrors from hidden to swap a unit at the hidden battlefield with a unit at a different location?

Ruling: Yes. Although hidden cards normally must target only the battlefield where they are hidden, Smoke and Mirrors explicitly requires choosing "another unit you control at a different location." This targeting restriction makes it impossible to fulfill the ability using only units at the hidden battlefield, so the exception in Rule 811.1.d.2 applies.

Nuances:

• This follows the same principle as the Tideturner example in the rules: when a hidden card's ability explicitly requires targets at different locations, the standard hidden targeting restriction is waived.
• You must still choose one unit at the battlefield where Smoke and Mirrors is hidden, and another unit at a different location to satisfy the "different location" requirement.