Description of problem: If you download the install media for F10 and/or create a net-install mirror, preupgrade can't use any of the data there (because it uses Everything and install media uses Fedora). Having a way to automatically pickup the packages from a local repo. would be nice.
This is silly. If you already have install media, you can just use that to upgrade. If you haven't burned it yet, you can use the hdiso install method. The entire point of preupgrade is to *avoid* the need to download and burn the ISO. The process is identical beyond that. Still. If you're dead-set on using the media, you can follow the section in the README that describes creating custom distribution entries in releases.txt, and use a url like file:///media/Fedora... But I'm not adding UI support for this to preupgrade.