I've sharpened bypass pruners without disassembly and your inquiry made my old mind re- think " is there a better or at least a different way "? And yes there is. I suspect this won't be for every bypass pruner design but it did work on my vintage pruners.
I determined, that when in actual use, the last 1/16" or so of the bypassed jaw, which protrudes above the cutting edge, was of no value on this pair. So using my bench grinder with the jaws completely closed and locked, that bypass jaw top edge was ground simultaneously when touching up the sharpened jaw. With that modification the the two jaws become one in that respect when completely closed and when sharpening ( they - it ) can be assumed as one blade.
The fine file used in a draw file motion followed by 600 grit wet / dry and the file as a sandpaper backer it could be used to shave but that would be rather awkward and scary I suspect.
Once modified sharpening will be a snap until I'm too old to use them.
