best is to get a pair of diagonal cutters yes, if you need to do this frequently you can find cutters specialised for this stuff who have a very thin side, so that it can fit between the cables and the cable tie, but that's only if you'd really do this often, otherwise it's best to just get a cutter, and put it's tops between two cables when you cut the cable tie, that way you cannot slip, it's hard to draw an ascii art image of it, but I hope u get the idea.