Whether you use snakebite or not, always make sure to backup your save folders first (named 287700 and 311340) located in Steam/userdata/(random numbers)/

Snakebite: Extract my file, select the .mgsv file you want from the SB install menu.

Manual: Extract my file, navigate to the skill you want, take the MbmCommonSettings.lua and put it in your 00.dat Assets/tpp/motherbase/script to overwrite the old file. 00.dat is in steam/steamapps/common/MGS_TPP/master/0. You can unpack 00.dat with the QAR Tool.

Watch this if you don't know how to use the QAR Tool. The description has links to download. Make sure to update the dictionary like the video shows you.
https://www.youtube.com/watch?v=VbI8lDsiSM0&feature=youtu.be