I doubt I would be able to identify a lynx at a distance so "tips from the trenches" as it were but is it not the same as any other system you are going into cold? Basically find some hardware docs/software development kits ( http://www.monlynx.de/lynx/
-- they do not seem quite so ROM hacker friendly as something like no$gba docs or even official SDK docs sometimes are though) and hope you have enough general low level computing knowledge to do some damage. Offhand I am not sure if any of the tile editors support it (TilEd2002 does not explicitly have it) but it is probably similar enough to another format that you can get something done and if http://code.google.com/p/tiledggd/
can not get something done I will be stunned (it seems like RGB arrangements).
The game cart seems directly memory mapped and it made no mention of banks (though it could have happened) and no mention of a filesystem for the ROM image (though it could also have happened).
On the level stuff though when reading through those docs I saw the hardware has collision detection which is fairly rare to have but quite nice at the same time.