ediff-before-session-group-setup-hooks is a variable defined in `ediff-mult.el'.
Its value is

  • This variable may be risky if used as a file-local variable.

Hook run before Ediff arranges the window for group-level operations.
It is used by commands such as `ediff-directories'.
This hook can be used to save the previous window config, which can be restored
on `ediff-quit', `ediff-suspend', or `ediff-quit-session-group-hook'.

You can customize this variable.