The documentation for using R in Databricks states that the session can be configured by modifying the /usr/lib/R/etc/Rprofile.site file. This works for most things, however the repository URLs set by the `repos` option is overridden by another script that's loaded from a temporary directory.
As described in this Stack Overflow answer, this second script /local_disk0/tmp/_CleanRShell.*.r sets the repos using the value of an environment variable DATABRICKS_DEFAULT_R_REPOS. This is useful for configuring custom R repository URLs to be used by default. However, given it isn't documented anywhere, I'm concerned its behaviour may change in the future without notice, or it may be removed completely.
Is this environment variable supported officially? If not, what is the recommended way for changing R repository URLs in Databricks?
