Just seeking some clarification on this scenario.

If I have 2 identical units of stormtroopers (A and B) is this legit.

Activate unit A - move/shoot etc.

At the end of the activation use change of plans to exhaust strormtrooper B's card and reactivate unit A?

Essentially allowing the first unit to get 2 moves in the turn?

Yes

Change of Plans

Yes, identical deployment cards have the same cost and same traits, so there is no problem using it. It's even better if the group you exhaust to ready this group has less figures remaining.

Be aware that you "exhaust" one deployment card to "ready" another one.
You don't get to activate Unit A straight away. You get to ready Unit A, then in your next activation you can use them.

So unit A can get a second activation during a round... but you don't get to just do two activations at once.

This card is most useful when you have one squad that's almost dead, and you'd rather exhaust that one to have another activation with a different full health unit. Or if one unit is way out of position.