I got a little impatient and decided to open it up today before my SSD arrived.
Good news though! Our thoughts were correct! The CPU is socketed (upgradable) in the 2019 27” iMac. :D
I powered it on and booted up the OS and everything ran smooth as butter with the newly installed i9 9900k.
I just need to get my SSD so I can close it up and start using it.
Thank you everyone for all your input and advice!
Chalk this up as another win for the repair revolution :D
-Zachary