I would consider not mucking with the official repositories and instead create your own. Any directory of RPMs can be turned into an RPM repository for Yum with the
createrepo command. So, after you gather your RPM's in one place, run
createrepo in the location:
createrepo -dp .
./repodata sub-directory will be created. Yum pulls the necessary metadata from this location to find the packages your client is looking for, so this entire directory will need to be exposed to the client in the same way your existing ISO based repositories are currently.
createrepo man page:
createrepo [options] <directory>
Output xml files in pretty format.
Generate sqlite databases for use with yum.
Note: I just like the "pretty" format option in case I have to get into those files and have an edit by hand.