Joseph DeGarmo :
So I recently found out about how the Windows 10 upgrades will roll out. Because of that, I have not yet reserved the upgrade, but will do so very soon. I may not be expecting the upgrade until September! Being that Windows Insiders who installed the tech preview will be the first to receive the upgrade, is it possible to install the tech preview on a new partition or hard drive alongside Windows 8.1 and receive the free upgrade that way while keeping both OSs?
Yes, if you install the Tech Preview now. My secondary laptop is like that, but with Win 7 and 10.
THe Win 10 Tech Preview will simply be rolled over into the final release version. You don't need to do anything.
However, if you wish to continue using that, you must remain a participant in the Insider Program. Which means you get all the updates and changes pushed on their schedule, not yours.
In effect, you are a permanent beta tester.
If you wish to opt out of the Insider Program, eventually that particular install will become invalid. You'll have to either roll back to Win 7 or 8, or upgrade an existing 7 or 8, or buy a retail Win 10.