Of course you can.
And, Deactivating it's not strictly required, since you have 6 activations available so, even if you forget to Deactivate, you can reactivate again (unless you forget to Deactivate for 5 times...). However, if you Deactivate first, the advantage is that you won't even consume an activation when you'll reactivate on a new system so, if best if you do it, if you can.
