IverntechMGN12 300mm 400mm 450mm 700mm Linear Rail Guide with MGN12H Carriage Block for 3D Printer and CNC Parts MGN12H Linear Guide AW014 1

How hard is it to trim these down? I need a length of 440 mm and would probably be getting a 450 and trimming 5 mm off each end. what tool would be

What size t nuts do you use

Are the holes in the carriage threaded?

Are these bearing blocks pre-loaded?