IIUC (I work for Red Hat but not on how sources are distributed), there is absolutely no change in practice.
CentOS Stream RPM sources are stored in GitLab therefore the whole history is available including past minor releases of RHEL. The only change is that the repositories will not be mirrored to git.centos.org.
git.centos.org (g.c.o) has been the historical canonical local for RHEL sources that have been exported out of Red Hat. On any given package you would see several branches, one for each major release and other organizational artifacts (e.g. c7, c8, c9, etc). Initially CentOS Stream 9 was exported to g.c.o as it wasn't a true upstream in the full sense of the word, but with CentOS Stream 9 that changed. c9s is developed in full on GitLab, and now c8s as well, while the final RHEL sources for those packages are still output to the c8 and c9 branches on g.c.o.
What changes here is that Red Hat will no longer be exporting the c8 and c9 content to any git platform (c7 will continue as exists until its EOL). Customers can access sources as needed via the Customer Portal and CDN repositories, but sources in git form will not be publicly available for those artifacts. Moving forward, only c8s and c9s sources will be available, and g.c.o will not see any updates for EL8 and EL9.
While most (I'd estimate at least 95%) of the platform will match in terms of NEVRA between versions available in CentOS Stream and their RHEL counterparts, there are some packages that will not due to the way they are developed.
I don't think it will be much more difficult to obtain.