the latest versions of LimeSurvey have modified the home page:
the logo is no longer displayed, which may imply that you will be able to put your own logo.

This is possible by modifying the source code of the files linked to the display of this page, but it is not recommended.

As indicated in this topic (even if a bit old):
https://forums.limesurvey.org/forum/design-issues/81473-user-log-in-page#202983

A setting via an interface like for themes would be judicious.
We could associate it with the setting of the administration theme with a part dedicated to the login page.

If we wish to indicate CGU specific to the use of LimeSurvey within our Company/Association/University, etc., we should indicate it before users log in.