I have received a few PMs about replacing mouse switches, since I noted how much better the Wow Joy Pen mouse is with lighter switches.
Old mice are easy to find for a dollar at yard sales and thrift stores, and you can probably guess how much use they have seen by the shine, or lack of shine.
A lot of ball mice are like new, even if they are 10 years old.
I will not go into assembly and dis-assembly here, since they are all different. If you can't figure out how to crack the case open, you probably shouldn't be doing this, anyway. Often, there are screws hidden under labels, stickers, or rubber feet. The feet usually go back on pretty well, if you are careful.
Inside, you will find some number of switches like the ones shown here. Most are the same size, with 3 connections on the bottom (circuit board) side. Verify that yours are right, they are generally pretty standard. I used Omron switches from a 10-15-year-old Logitech ball mouse in a brand new Joy Pen knock-off.
You will need to un-solder the switches from the boards on both mice. You are probably only concerned with the 2 primary switches. You can wreck the donor board but be careful with your recipient. I use the braid, but a sucker is probably better. I only have a sorry cheap soldering iron, if I had better gear this affair would have been much easier.
Some of the switches have only had 2 leads soldered, the ones in my photos show all 3 soldered.
After you remove the original switches, the others should just substitute back into the same holes. Be sure to clean up enough old solder so that the leads will insert fully.
I have shown a board with the micro-switches attached, and circled one of the switches and numbered the connections 1-2-3 so that you can see how they look from different angles.
This is not a very comprehensive guide, but may be enough if you can figure stuff out on your own. I will try to upgrade it later. Good Luck!