I agree with Hadden. Replacing Shell32 is likely very dangerous. I would try the UxThemeSignatureBypass tool installer Mr.GRiM posted in the AeroGlass for Windows 10 RS1 thread. All you need for that to work is to disable Secure Boot in you system BIOS.

It's likely the best method atm as it doesn't require you to modify system files. It simply injects the UxThemeSignatureBypass.DLL into your registry to disable theme signature requirements [allowing custom .msstyle themes to work].