Hi Rob,

sorry for the late reply!

»Will this allow you to keep all of the current subdomain name blogs? And will this switch all new registrations to subdirectory?«

This will not remove any of the existing sites of the multisite, and will not change the default registration from subdomain to subdirectory.

»Also, will it prevent new sign ups on the front end?«

Yes, the first step does this.

Cheers,
Florian