Do all your low rez files have the same file names as the originals? They don’t have to be the same format, just the same file name.
If so, it’s rather easy to replace everything.
Fist use the project manager to make a new project with just the final sequence and the video files required. You don’t have to copy the media, just make a new project file.
Open this new slimed down project.
Select all your footage in the project panel, and right click Make Offline. Don’t delete the files, just make them off line.
Then right click all the files again and select “link media….” and select the high-rez file will the name matching the file it’s asking you for. (it’ll say “where is xxxxxx”)
Done!
you can also do this with the “replace media” command, but you have to do it one file at a time. My way you can do all the files at once.