Advice on painting a vehicle and "roping" the winshield gasket??

Will be using a monstaliner textured paint on the old beast... and although the window gaskets are not brittle or cracked they are stiff after 43 years of existance. I don't want to buy new rubbers as they literally cost an arm and a leg - vehicle in question is an old International.

Anyways, does anyone have any advice on what I might be able to use to make the rubber more pliable without risking cracking? ...and how far do I have to lift the rubber off the sheetmetal when "roping"? I assume that 1/8" nylon weedwacker cord might work? Anything else that other have used? Also, is the cord removed while the paint is tacky, or completely dried? Don't want to risk the cord getting "glued" in if the paint completely dries hard around the cording. Thanks!