I create installation package from several *.wxs files where several of them are generated by heat utility and contains ComponentGroups.
Now I need to create installation package for per-user installation.
RegistryKey should be added to each component in case of creating of per-user installation package by Wix.
How to add RegistryKey to all components in files generated by heat utility?
There is no short way. You need to apply XSLT transformation to your heat generated file, and add the attributes.
In order to do so, you need to pass -t yourTransformation.xslt to heat.exe,
I blogged about something similiar in the past: http://chriseelmaa.com/xslt-wix-heat/ That's an example how you can add ServiceInstall element to specific wix:Component.
You'd probably want to take a look at this too, in order to see how to add attribute to wix:Component: Copy node and add value to attribute with Xslt