Every build of Windows from Windows 8 build 8400 (the Release Preview) to Windows 10 build 9926 is compatible with the themes of the builds before it. What do I mean by this? Under Windows 8 RTM (9200), you can run 8400's theme natively along with the default. Under 8.1, any theme for 8.0 and 8400 can load. Same goes for early 10 builds. Under 9841, any Windows 8.1, 8.0, and 8400 visual style runs without many issues. This seemed to stop around 9926 due to the visual style engine changing, I assume. Here's three versions of aero.msstyles running under 9926 with no issues. (8400, 9600, and 9841 respectively)
If you patch uxtheme, you can run any 8.x visual style under 9926, but the caption buttons will be huge due to it being Windows 10, and most of the taskbar textures being missing due to msstyles losing the ability to skin the taskbar as well. Here's Simplex's Windows 7 Aero visual style also running under 9926.
And I will reiterate, this will also work with any version of Windows between 8400 and 9926, but you can not use themes newer than the OS you're using. (i.e. 9841's aero.msstyles under 8400) And if there are builds before 8400 and after 9926 that also work with this, please correct me.