Also falls es wen interessiert, so funktioniert's:
# Obtain the MSIL for the provided assembly
From a VS.NET command prompt, enter the following:
c:\>ildasm providedAssembly.dll /out

rovidedAssembly.il
# Rename/move the original assembly
I just tack on ".orig" to the filename.
# Create a new assembly from the MSIL output and your assembly keyfile
Assuming you already have an assembly key pair file (if not, see #1 in previous steps), do the following from a VS.NET command prompt:
c:\>ilasm providedAssembly.il /dll /key=keypair001.snk