Changing .mp4 suffix to .mpg works to make .mp4 usable, but is it a dangerous kludge?

[macOS 10.14.6, Premiere 14.0.3)

I'm working on a 4K project with a lot of .mp4 Broll, and these mp4's are unusable in the timeline as they 'disintegrate' into green and broken images.   I've tried rewrapping into .mov using Cineplay and other tools, but the problem persists.   Trancoding to ProRes would be wonderful, but I have neither the disk space nor the time to transocde hundreds of hours of these .mp4's.   But what HAS worked, is simply changing the .mp4 suffix to .mpg.   This allows the clips to behave normally, with no more green noise.   But this is a large multi-episode project, so I'm wondering if this simple trick is a cheat - am I shooting myself in the foot?  Is this problematic?   Is there a better way?