How can I remove a strong name from a 3rd party assembly that I do not have the source code for, maybe using ilasm/ildasm (since it is possible to add a strong name using ilasm/ildasm)?
Generally, it seems to be possible, since this tool seems to be able to do this.
Just use a tool to do it for you, doing it manually will probably take you too much time and hell, if there are tools out there then why reinvent the wheel?
Personally I have never used SNRemove but here is a list of tools I generally use:
EDIT: simple-assembly-explorer/SimpleAssemblyExplorer.Core/Assembler/Assembler.cs - this class should give you an idea of how strong name keys can be removed from strong named assemblies.