Look for Fiskars shears (with mightily sharp needle points) and do the cut over a bright lightbox. Steady, confident hands will do it. Of course less of a margin for stuff ups when cutting 35mm than 120.
Fiskars can be bought from hobby shops that have stuff for sewing. I have had mine for more than 15 years.
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Lab operators are not necessarily deadly accurate, as witnesseth a lab chopping through the last frame of a roll of 120 film! I had plenty to say (none of it repeatable here). I've never cut through or ruined any of my own trannies. Just my fingers...