For a corporate environment, I want our R users to use our local repository only. I have made corresponding required changes to Rprofile.site, .Rprofile, and repositories files as suggested by other posts and it works fine for changing the repository option only to the local one. However, a user is still able to select a CRAN mirror by selecting "Set CRAN Mirror" from the menu or by running "chooseCRANmirror()" command and when she does either of these, it will add standard CRAN repository as a repository option again. What can I do so that users don't see/get the default options for CRAN mirrors and as a result can no way change the local repository?
EDIT: As @Dason says, I don't want to stop the expert user from changing the repository option or others. I want to disable choosing mirrors just to ensure that users will not be able to access remote repositories (and download a package from there) by mistake.