It turns out; you can actually upgrade your unsupported Windows Phone to get the Windows 10 Creators Update mobile OS after all. Yes, despite the fact Microsoft said only 13 Windows Phones will be eligible for the upgrade. You can in fact upgrade your unsupported (not within the list of 13 supported) Windows Phones to the latest Windows mobile OS.
Just how do you go about upgrading unsupported Windows Phones to get the Creators Update? Well, it is not a hack, if that is what you are thinking. Actually, Microsoft itself has given out a guide on how you go about upgrading unsupported devices. The argument the company puts forth is that while these devices are not eligible for further feature updates, they are still supported by Microsoft as far as cumulative updates go.
Below is a walkthrough on how to get the Creators Update as cited by MSPowerUser.com
How to upgrade unsupported Windows Phones
Scenario I: You have an Unsupported Device but already on Windows 10 Creators Update (Build 15063): If that is your device, go to Settings > Update & security > Windows Insider Program and move over to Release Preview ring. That way, you will continue getting Cumulative Updates for Build 15063 and your device should be able to take up Build 15063.251.
Scenario II: You have an Unsupported Device but you are not on the Windows 10 Creators Update (Build 15063): If that is your device and you need to get the Build 15063, you must first join the Windows Insider Program on your device; either the Fast or Slow ring. Once you do that, your device will start taking up multiple ‘hops’ until it gets to Build 15063. If your device is a bit older, it will have to work its way from the Windows 10 November Update (Build 10586), then Windows 10 Anniversary Update (Build 14393), and finally to Build 15063. When it gets to Build 15063, go to Settings > Update & security > Windows Insider Program and move to the Release Preview ring so that you can continue getting the Cumulative Updates for Build 15063.
Scenario III: You are on an Unsupported Device and you want to return the device to the supported state: You will need to remove your device from the Windows Insider Program by using the Windows Device Recovery Tool to re-flash your device and use the Upgrade Advisor app to get back to Windows 10 Anniversary Update (Build 14393). From there, your device will receive the latest Cumulative Updates for the Windows 10 Anniversary Update going forward.
For clarity purpose, Microsoft is not stopping you from upgrading to the Creators Update, you will in fact get the Cumulative Updates going forward.