@Edgemeal This verification exists to prevent REAPER from loading two ReaPacks at the same time. It also prevents new users from installing it in the wrong directory (eg. Plugins in Program Files) or under an arbitrary filename by mistake.
SWS does a similar check for the same purpose (preventing two SWSes from being loaded).
https://i.imgur.com/ep3BUkV.png
You can rename the copy to be something REAPER won't attempt to load such as "reaper_reapack64.dll.old".