A vinyl window scoring tool useful for rapid modification to the width of various standard sizes of flat vinyl trims to a smaller chosen width. Further, the tool may be used for edge-guided scoring on either or both sides of vinyl window flush-fins. And similarly, also for edge-guided scoring parallel to existing drywall window casing and sill ends. The tool comprises a slitting-component and a scoring-component hinged together in front by a coupling pin inserted through aligned holes. Each component possesses a laterally moveable and securable blade-hold apparatus including a captured blade. An element spanning both components provides controllable pressure on the vinyl trim by the aligned blade points sandwiching the trim as it's pulled through. Removal of the coupling pin disconnects the scoring-component and permits its independent use for modification facilitated by edge-guided scoring techniques on flush-fins and drywall casings. The vinyl window scoring tool may be reassembled for use by a left handed installer.