How do I download a macOS beta point update? What this question is not about


Downloading macOS Developer Beta Access Utility
Downloading a stable/GM release of macOS
Downloading the .0 release of a new macOS beta (when it is released at WWDC)


Say I want to install a macOS beta point update to a Mac that is never online (say if I had a lake house Mac or something). How would I download a .dmg or something so that I could install it on another machine. The macOS Developer Beta Access Utility just starts the update process on the machine it runs on.
I'm sorry, you're question is still a bit confusing to me, but I'll take a stab at it:

Your best bet is probably to comb through the listings you'll find in the Software Update catalogs found in Seeding.framework. That is:
plutil -p /System/Library/PrivateFrameworks/Seeding.framework/Resources/SeedCatalogs.plist, and (since we're talking Dev builds), probably
curl -Ls https://swscan.apple.com/content/catalogs/others/index-10.14seed-10.14-10.13-10.12-10.11-10.10-10.9-mountainlion-lion-snowleopard-leopard.merged-1.sucatalog | plutil -p.

You'll then need to grep around for the packages you're looking for; they're not always named the same, but if you grep for macOSUpd, you'll find the necessary packages, i.e., http://swcdn.apple.com/content/downloads/46/21/041-19988/kct9qwin7h5nz0awoc9ke03m2s7qp4q7t9/macOSUpd10.14.2ForSeed.pkg.

Does that help?