I have a class that has methods like:

   [DllImport("wfdb.dll")]
   private static extern int setsampfreq(double freq);

The wfdb.dll file isn't in the current directory nor on the path ... so I
want to qualify it with the path name, for example:

   [DllImport(@"c:\foo\wfdb.dll")]

However I don't know until run-time what the path is, so I want to set this
path in the static constructor for my class.

I can use class_type.GetMethods() to get MethodInfo[] and
method_info.GetCustomAttribute() to find the existing DllImportAttribute
instance for each method, but I can't change the DLL filename using
dll_import_attribute.Value because the Value property is read-only: the
filename can be defined only when then DllImportAttribute instance is
constructed.

I therefore want to create a DllImportAttribute instance at run-time and
associate it with the method. Unfortunately I don't see how to associate a
new attribute with an existing method at run-time.

Can this be done?

Or, can I do it only by creating the class and its methods from scratch, by
using AssemblyBuilder and TypeBuilder and MethodBuilder?