The Hex spell reads (PHB, p. 251):
You place a curse on a creature that you can see within range. [...]
If the target drops to 0 hit points before this spell ends, you can use a bonus action on a subsequent turn of yours to curse a new creature.
Hex still requires range and sight requirements to be satisfied when re-applying because of the first line of its description but I am uncertain whether the targeting limitations apply when the spell is not being cast?
The precise situation I am thinking of is moving Hex to a target that is visible through a transparent window. I suspect the answer is no but would appreciate a deeper understanding.
A related component of this question is whether moving Hex is considered to be moving the effect or having multiple targets.