Yes. If the seat remains empty you can just move over.
Pets need to be declared in advance at least 48 hours prior to departure so if the seat is still empty by then try if the block is lifted and you can assign it to yourself. Failing that, try again when OLCI opens at 24 hours before departure. And finally, you can also speak to check-in staff or gate agent and get the seat assigned if still empty at check-in as you won't be able to change seat selection on your own at one hour or less before departure time.