This unlocks the playable avatar (the one you create at the beginning of the game) to be chosen as a character without first having to complete the final mission.

This is for game version 1.09 or 1.10.

Files:
Due to the small file sizes there is only one upload. It contains the lua files for both the base game, the Stable Mods Compilation by Dolphin74, and Infinite Heaven by tinmantex. SnakeBite files are included for all three.

Known Issues:
The avatar functions mostly like playing as another soldier and not Snake. You still getting the voice acting, but some events won't kick off. I've noticed this specifically with the Visit Quiet side mission.

How it's Done:
In case you want to add this to a compilation, or want to make the changes yourself for another reason, you can follow the very brief instructions below.
In the 00.dat file go to assets\tpp\script\lib and open TppTerminal.lua; on line 877 you'll find the following.

if n>=TppDefine.STORY_SEQUENCE.CLEARD_THE_TRUTH then
vars.isAvatarPlayerEnable=1
end

This unlocks the avatar whenever the mission The Truth is completed. You can either change this to the following, or insert it above/below the existing if statement.

if n>=TppDefine.STORY_SEQUENCE.CLEARD_ESCAPE_THE_HOSPITAL then
vars.isAvatarPlayerEnable=1
end

This will unlock the avatar after completing the Escape The Hospital mission.
Special thanks to TheReciprocator for Unlock Playable Avatar that set me on the right track for getting this to work.