If you now use 5 pin Midi via an USB Device, the Midi device name did change, and hence there is no way "see" the original device name in Reaper any more.
But you can manually change the input and output Mid Device ID in the Reaper "Midi devices" menu to match the old setting. After that the original project should run as before. (For loosely related technical stuff see ->
https://forum.cockos.com/showthread.php?t=219792 )
-Michel