I would use a fine toothed saw such as a coping saw or a hacksaw.

I've cut this stuff myself with a hacksaw and it works well - just don't shove too hard when / if the saw snags. If you do you can shatter the plastic. You need a steady hand to get a nice straight line, but it is possible.

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1992 W201 190E 1.8 171,000 km - Daily driver
1981 W123 300D ~ 100,000 miles / 160,000 km - project car stripped to the bone
1965 Land Rover Series 2a Station Wagon CIS recovery therapy!
1961 Volvo PV544 Bare metal rat rod-ish thing

I'm here to chat about cars and to help others - I'm not here "to always be right" like an internet warrior



Don't leave that there - I'll take it to bits!