If you wish to lose RMA option and open the mouse, there are following DIY options:
-solder another switch;
-open the existing switch and try adjusting the spring inside it, like shown here
. But in order to reduce required actuation force instead of flattening the shown section you should curve it a little bit more (be careful);
-try gluing something thin (preferrably slick, too) onto a clicker of an upper shell - that'll reduce button travel and make it a bit easier to click. Don't use if travel is already too short.