32/64 bit registration is driven by each Installer Project's Custom Actions
Separate projects are provided and configured for 32-bit and 64-bit builds.
Change Property setting Run64Bit to False for 32-bit Office registration
Right-hand click on each category to change property as per screenshot below
Install > Primary Output > Properties > Run64Bit = False
Commit > Primary Output > Properties > Run64Bit = False
Rollback > Primary Output > Properties > Run64Bit = False
UnInstall > Primary Output > Properties > Run64Bit = False
Settings are then configured automatically by the installer class
Environment.SystemDirectory = C:\Windows\SysWow64 for 32-bit install
Environment.SystemDirectory = C:\Windows\System32 for 64-bit install
Registry = HKEY_CLASSES_ROOT\WOW6432Node\CLSID\.. for 32-bit install
Registry = HKEY_CLASSES_ROOT\CLSID\.. for 64-bit install