If you search on the net, you will probably find detailed polishing instructions on the Mk II factory trigger, including exact measurements etc.
Personally I wouldn't trust myself trying to lighten it up by reducing the dimensions. But you might find out that simply polishing the mating surfaces a little with some Flitz might help smooth it up. Could be just a tiny burr on there or something
Worst case, if you screw up, and make it dangerous, you can go with one of the replacements as mentioned above.