Tweaks (minimal configurations to make a game functional) can be installed (to /usr/share/steamtinkerlaunch/tweaks) from the optional external repo steamtinkerlaunch-tweaks

If a game tweak in this dir is found steamtinkerlaunch loads that tweak before starting the game and opens a Notifier

Support for user defined tweaks is still built in, but unlikely it is worth any documentation.

for SBS-Tweaks see SBS-VR