Can I still use Samsung Smart Switch if my new phone is already activated?

[Android Central Question]

I have a Samsung GS4 and have just bought a Samsung GS9+. I want to use Samsung Smart Switch to move my "stuff" to the new phone. The instruction says to move the data before activating the new phone. The new phone only gives me the option to "activate now?"--I can't get to any other window or skip this one. If I go ahead and activate it will my deactivated old phone still be able to work with Smart Switch? Please help me figure out what to do! Thanks