If you want to replace another GS rename the twoXXX folder and all the files inside to match the GS you want to replace.

Weapon ID's:

https://mhw.poedb.tw/eng/wp_weapon

If you want to replace another CB rename the caxeXX folder and all the files inside to match the CB you want to replace.

Weapon ID's:

https://mhw.poedb.tw/eng/wp_weapon

If you want to replace another SA rename the saxeXXX folder and all the files inside to match the SA you want to replace.

Weapon ID's:

https://mhw.poedb.tw/eng/wp_weapon