Asymmetric key to import assemblies

To import the System.DirectoryServices assembly requires the following commands

create asymmetric key asmKey_DirectoryServices
from executable file = 'c:\Windows\Microsoft.NET\Framework\v2.0.5072
\System.DirectoryServices.dll'

create login asmLogin_DirectoryServices
from asymmetric key asmKey_DirectoryServices

grant unsafe assembly to asmLogin_DirectoryServices

This creates a new login. If I need to import several assemblies, is there a way to use only a single login with multiple asymmetric keys?