[HKEY_LOCAL_MACHINE\WIM_Software\Microsoft\Windows\CurrentVersion\Themes]
"InstallTheme"="%SystemRoot%\\resources\\Themes\\AeroNoBackground.theme"

This is correct, rigt? Double backslash only for disk paths.

[HKEY_LOCAL_MACHINE\WIM_Software\Microsoft\Windows\CurrentVersion\Themes]
"InstallTheme"="%SystemRoot%\\resources\\Themes\\AeroNoBackground.theme"

This is correct, rigt? Double backslash only for disk paths.

I think so. Its is an escape character probably because reg.exe is not smart enough to determine the difference between physical (disk) paths and registry paths.

This is correct, rigt? Double backslash only for disk paths.

Yes, that's correct as for a double backslash.

I would use a Reg_Expand_SZ at a %SystemRoot% entry.

The reading application has to support this too.

However, does this relate to installing a theme? http://www.wincert.net/forum/topic/9658-themes-how-do-you-do-it/

That's another question. I don't know.

Desk.cpl seems to install a theme.

http://www.wincert.net/forum/topic/7377-trick-how-to-set-windows-theme-from-command-line/

OT was Double backslash but now we went rampant on themes.

Think this OT was solved here:

I don't doubt %ResourceDir%. I doubt the type Reg_SZ.

me three

I use a self created themepack and it does all I need