Read register value and replace

Well I want to make a 'SectionOutPut' which first reads a register key HKCU "\Software\BioDuo" "BioDuo" "C:\Program Files\BioDuo.exe"
But it should first read that register file, and after that it should replace the "\BioDuo.exe" with "\Skin\"
And in that map NSIS should install the files. but my problem is how do I do that?

1. Use ReadRegStr
2. Use GetParent (from NSIS manual)
3. Append "\Skin" by using StrCpy

Function .onInit

 ReadRegStr $R0 HKCU "Software\BioDuo" "BioDuo"

 Push $R0

  Call GetParent

 Pop $R0

 StrCpy $INSTDIR "$R0\Skin"

FunctionEnd

-Stu