Custom git diff tool in gitlab

Gitlab 12.1 CE. Exist whether way to add custom git diff tool in gitlab? Im look into GIT_EXTERNAL_DIFF= before call my script on bare repos ( on my gitlab server ). When im test GIT_EXTERNAL_DIFF with custom diff tool - it works on local machine.

So, can, in principle, Gitlab work with custom diff tool?

So the answer is Yes, but it cannot be completed before this ticket is made after that, add a custom diff tool looks easy.