I like the posh-git powershell env for git but on some (very large) repositories it noticeably slows down the ps prompt.
I'd like to know if it is possible to disable it on certain specific repositories
For performance, they do suggest a way to disable file status per repository:
https://github.com/dahlbyk/posh-git#customization-variables
Note on performance: Displaying file status in the git prompt for a very large repo can be prohibitively slow. Rather than turn off file status entirely ($GitPromptSettings.EnableFileStatus = $false), you can disable it on a repo-by-repo basis by adding individual repository paths to $GitPromptSettings.RepositoriesInWhichToDisableFileStatus.