[mono-cecil] Can I inject IL code into .net assemblies?

[jasper]

Hi,
Can I inject code into .net assemblies like System.Windows.Forms or
System.Web? If yes, what should I do to get it working?
I tried to inject code through cecil but it failed.

I tried this
            AssemblyDefinition assembly =
AssemblyFactory.GetAssembly(typeof(System.Web.UI.Page).Assembly.Location);
but it failed.
Any help would be nice... Thanks..

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mono-cecil