Can I replace a still frame segment at the end of an MP4 without re-encoding the entire video

I have an MP4 I made years ago and I lost the original .pproj file that made it.  All I need to do is take the last 5 seconds of the video, which is a still frame, and show a new still frame.  Can I do this without having to reencode the whole thing and lose quality?  I'm thinking some kind of adaptive encoding that only encodes what is changed.  Does premiere pro support this function?  Thank you.