"Freezing" settings ?

I am installing LO on self-service Linux computers in a library.

Which configuration files do I need to “freeze” with chattr to ensure that the default settings are not modified by the users ?

Assuming every self-service point has its own user ID it will also have its own user profile. By default it contains most of the folders listed under >Tools>Options>LibreOffice>Paths. You may copy a default user profile to the respective location and block write access for the (abstract) user to it.
See https://wiki.documentfoundation.org/UserProfile. Specifically regard chapter 3 and tere 3.3.

===Edit1 2018-11-30 18:20 CET===
The German wiki page concerning the user profile is telling:

Unter Linux können Sie den Variablenwert von
z.B. auf
ändern, um einfach ein anderes lokales Verzeichnis parallel zum ursprünglichen für diese Installation einzustellen, oder z.B. auf
um ein einziges globales Benutzerprofil für alle Benutzer dieses Systems gemeinsam einzustellen.  

This part is missing in the English page.

Is there any risk of LO malfunctioning if I make all those folders read-only with a chattr -R +i /home//.config/libreoffice/4/user command as root ?

I’m afraid there’s a risk of LO not starting at all in that case. LO requires write access to its profile IIRC.

You could instead create a startup script running when user is logged on to copy default settings files into the LO user folders. Or, if you prefer, a “logout” script to erase any user modification.

This is the fall-back plan if I chattr .config/libreoffice/4/user causes problems with LO: save a clean copy of .config/libreoffice/4/user in another directory, chmod’ed to RO and"frozen" with chattr, which the script will cp to ~, and chmod to RW

After some testing with a portable version I feel sure again that LibreOffice accepts a user profile without write access. I observed the registrymodifications.xcu specifically.
@rolgiati: Please report here your definite experience. You can answer your own question for this purpose.

That wiki page’s hint to share a user profile among all users (“globales Benutzerprofil für alle Benutzer”) is very ill advised. In fact it doesn’t work (LibreOffice refuses to start a second instance with the same UserInstallation path) and if it would the configuration would be scrambled by different instances trying to write to the same profile. Which exactly the English page explains.

You want to read the answers to Admin-Configuration.
And also take a look at the wiki Deployment and Migration.