Modifying Assembly Attributes (.NET)
 

Is there a way to modify Assembly Attributes of existing assembly?
What I want to achieve is to add InternalsVisibleTo attribute to expose assembly's internals to my library.

You can use something like Mono.Cecil to rewrite parts of the file and then save the changed file. Check out Mono.Cecil here:
http://www.mono-project.com/docs/tools+libraries/libraries/Mono.Cecil/

dnlib is another similar library:
https://github.com/0xd4d/dnlib

You should be able to alter the attributes of classes and such to your needs to make it work as desired.

I accomplished the task with Mono.Cecil, thanks.

By the way, I guess it's not possible to import .NET 4.0 module into .NET 2.0 assembly?

You can if the 4.0 module exposes what you need via COM. The 2.0 assembly can then use the object(s) via COM. A straight import is not possible though because of the .NET version mis-match though.

You can see more info on how to accomplish this here:
http://www.codeproject.com/Articles/204406/How-To-Use-a-NET-Based-DLL-From-NET-Based-Appl

Thank you very much atom0s. Very useful.

Sorry to bother you, but I have one last problem. The app stores resources in separate .dll file. I had to remove Strong Name from the .exe, but then I noticed that it won't load strong-named .dll. Why? What am I missing here?

These links may help some:
https://msdn.microsoft.com/en-us/library/s1sx4kfb(v=vs.100).aspx
https://msdn.microsoft.com/en-us/library/xwb8f617(v=vs.110).aspx

As MSDN states as well:
So from the look of things you are required to keep the strong-name on your exe in order for it to load those modules. Bypassing though, I am not sure. I tend to not ever really use strong names on anything I make so I've never personally had to deal with it.

Sounds weird to me. An exe without strong name should be able to load a dll with strong name. Anyways, strong name doesn't work as far as I know. You could just modify things and maybe hook StrongNameSignatureVerification if the program checks the strong name.

An alternative solution is to simply re-sign everything using your own strong name :)

I have read that paragraph, but as mr.exodia points out - the .exe has been stripped out of Strong Name, hence the question. Shouldn't it be able to load any strong-named .dll? Nonetheless, if I remove the Strong Name from resource .dll, it loads correctly then.