Question : Is there a setting that recognizes a finished clip and simply stitches them together or zooms through.. instead of doing a full reprocess?
There is no setting that prevents it, Premiere is not designed for that, it will be recompressed.
Is the reprocessing of a completed clip degrade it?
Unfortunately yes, recompression results in a loss of quality.
I have a free little program that stitches different mp4s together, on my former pc. I can't remember if it was glitchy, but it worked fine and fast on cellphone video clips, tying then all together without changing their original files.
This would be a great feature for Premiere or subprogram to add.