Yes you can. You are supposed to announce to the other players if you are making an amphibious assault (resulting in combat this turn) or an amphibious reinforcement (with NO combat in the contested territory this turn).
What’s more, if you do an amphibious assault, accompanying battleships can conduct shore bombardment and any defending artillery can take shots at your landing units. With an amphibious reinforcement, your battleships do not bombard and the defending artillery do not take shots at your landing units.
Battleships and defending artillery do not fire if you are offloading to a contested territory whether you conduct combat there or not. They only fire if you offload to a hostile territory.