You can either copy the files manually or patch the msi package using Orca.
Orca.exe is a database table editor
for creating and editing Windows
Installer packages and merge modules.
The tool provides a graphical
interface for validation, highlighting
the particular entries where
validation errors or warnings occur.
This tool is only available in the
Windows SDK Components for Windows
Installer Developers. It is provided
as an Orca.msi file. After installing
the Windows SDK Components for Windows
Installer Developers, double click
Orca.msi to install the Orca.exe file.
Basically you'll have to mimic the msi package behaviour: change the default files and re-register the component. There are four files for the RDC client 6.0:
You may have to change the localized folder (us-en). The folder should already exist. I have a localized version.
Extract the files from the list above using 7-ZIP from the RDP client packages. You first must unregister the DLL, delete the files, copy the new files to their location and register the new DLL.
Unregister the mstsc components using this command:
regsvr32 /u mstscax.dll
And register it with
regsvr32 /i mstscax.dll