Adding rules in a plugin?

I'm writing a GHC plugin that generates new rules. The top-level identifier for the new rules' LHSs is always the same and is imported from another module. One of the arguments in the rule's LHSs, however, is defined in that module. I'm creating rules and adding them to the mg_rules of the module's ModGuts. I don't see them in the .hi files (viewed with "ghc --show-iface Foo.hi"), and they're not getting found in modules that import the modules where I'm trying to generate rules. Am I missing a crucial step? For instance, do I need also to use `addIdSpecialisations` with the argument identifiers, and if so, need I replace all instances of those identifiers in the module or just some of them? Thanks, -- Conal