I would like to use a Redding Compitition Seating die or sleeve type seater, for a Swiss 7.5 MM x 55 K31. Since it appears that there is not a die manufacturer making a sleeve type seating die for this cartridge, my question is how hard would it be to convert an existing die to handle the Swiss 7.5MM x 55? Or is it even remotely possible for a current production die ( different cartridge ) to be used for this cartridge? What I am thinking is that there could be a dimensionally similar cartridge that may work for the Swiss 7.5MM?

If this is the same case as a 6.5 x 55, then a die modified for a 7.5 mm neck and stem may give you what you need. Check with Forster and Redding.