I think the Windows 10 default association is actually Windows Explorer, since Windows 10 is supposed to "mount" any ISO file you double-click and create a virtual drive from it. I'm guessing that ImgBurn has grabbed the association from Explorer.
You can shift the file association over to NXT 8 if you wish. First go to an .ISO file, right-click it, and go to Open With and then Choose another app
In the window which appears, first check the box at the bottom to Always use this app . . . then select Roxio Creator Application if it is there. Click OK, and you're done.
If the Roxio Creator Application hasn't appeared in the list yet, you need to go find it. To do this, select the blue More Apps link. This will show you a bunch more applications to choose from. If the Creator Application isn't in the list, select Look for another app on this PC
You're nearly there. An Explorer window will open into C:\Program Files. Navigate instead to C:\Program Files (x86)\Roxio Creator NXT Pro 8\Roxio Central (or NXT 8 if you don't have the Pro version) and look for roxiocentralfx.exe
Select that .exe file, click Open at the bottom right, and you are finally done. Your ISO files will all have a Roxio "R" on them, and double-clicking on one will bring it up in Burn Disc Image.
Was that what was wanted?