> I don't think this will work elegantly.
> 
> Static first makes a Structure (is make the right term?) and then makes a bunch 
> of other modules using it. A custom Structure will be needed to downcase the 
> keywords before inserting them into the hash table, so Static will need to be 
> duplicated as well.

Well I just duplicated Static to Static1 (and added Camlp4.Struct.Grammar where necessary) and replaced:
  module Structure = Camlp4.Struct.Grammar.Structure.Make Lexer;
by:
  module Structure = struct
        include Camlp4.Struct.Grammar.Structure.Make Lexer;
        
        value using { gkeywords = table; gfilter = filter } kwd =
            let kwd = String.lowercase kwd in
        let r = try Hashtbl.find table kwd with
                [ Not_found ->
                    let r = ref 0 in do { Hashtbl.add table kwd r; r } ]
        in do { Token.Filter.keyword_added filter kwd (r.val = 0);
                incr r };
    end;

This way, I redefine "using" to my liking, the only modification being the lower-casing on the first line.

Structure is then passed to other functors as usual.
Note that you need to compile Static1 with camlp4r because it is revised syntax (in ocamlbuild _tags this is camlp4r, use_camlp4).
This seems to work (you need the lowercase in match_keyword too btw): I have "acTIon" and "actiON" in the parser, and parses "action" in input files.

Cheers,
Matthieu