There are two categories of modification:

AESTHETIC: These mods include: Resin casted buttons, sticks, triggers, shells, cable plugs; paracorded cables, painted shells, etc.

FUNCTIONAL: Motherboard replacement, Snapback capacitors, Notching, etc.

Every mod exists for a reason, whether that be looking fly as heck expressing yourself not only via your gameplay but your controller as well or satisfying your technical needs and preferences with a specific technical mod. Every player is different!

This video by zenith SSBM does a great job explaining how to open up a GameCube controller. You can find similar types of videos on Youtube for other kinds of controllers.

You will need a Triwing Y0 screwdriver to open up the shell of the GameCube controller and a Phillips Head #0 screwdriver to take the triggers out. Here is another detailed guide.

Currently I only make full resin sticks. This means they are made 100% out of resin and feel slightly different than OEM rubber capped sticks.

This is normal due to micro scaling differences in resin casted parts. The easiest fix involves taking a small sliver of clear tape (regular household clear scotch tape works great) and placing it over the hole on the bottom of the resin casted stick. Then when you push the stick onto the stickbox, the tape will act to create a friction fit.