You can certainly serve the sucatalogs via both http and https -- IOW, yes, it is possible to have Apache serve the same files via http and https.
But the catalogs list URLs for the files that make up products: packages, metadata, etc. These URLs will be either http or https, and those URLs start with the LocalCatalogURLBase.
So I think you are in for some testing: Can you set up https, leave http also working, then change the LocalCatalogURLBase to be an https URL, and then do clients still using the http URL still _work_? I don't know the answer to that. I think it will work, but you'll need to test for yourself.
-Greg