I am working with an mp4 version of an edit and want to replace it with a ProRes (MOV). If I try and relink to the new file Resolve cannot find it (presumably because of the .mov file extension). Is there anyway to specify a specific file to replace rather than searching a directory?
Yes, there is, but without TC you'll have a problem. There is software to add a fake TC, like EditReady or Kyno on the Mac. I'm sure there is such software for the PC too. Have a look at these tutorials: