Second that! When I have to cut masking, I take a brand-new blade out of the pack, just for that purpose.
That’s a general principle for any knife or other edged tool, by the way-keep your knives sharp! As you note, you have to apply more pressure to cut, and that increases the risk of slipping and injuring yourself. I learned that rule when I learned to cook.
Or you could also apply a coat or two of a clear medium over the masks, like a clear acrylic. I use Future, myself, but there are many products available. The key is that this seals the edges of the tape, to help elminate paint bleed.
Also forgot to add, make sure you burnish the heck out of the edges to make sure they are down before painting. A toothpick, piece of sprue, or a fingernail will do. I don’t have a problem with paint bleeding through on my canopies. My problem is that I get in a hurry after the paint dries and remove the mask without getting the knife out and scoring along the mask, cutting through the paint and leaving a sharp line, instead of the ragged edge left by simply pulling up the mask.