Spellcasters can dismiss various spells, causing their duration to end prematurely. Do characters utilizing spell effects from magical items have the same capability?
Say, for example, my fighter activates his cloak of the hedge wizard (transmutation) to gain the benefits of enlarge person in order to gain an advantage in a fight. However, the fight does not go well and he is forced to retreat into a small tunnel (where even medium creatures would have to squeeze).
Can he dismiss the effect as a standard action like a typical spellcaster and get to the safety of cover?
No. the wand has taken over the role of casting and it has no direct control on the spell once it's unleashed.
Your fighter is stuck being large because he's not in charge.