That Caecilia is handled in a very weird manner by the framework, so you may have to play around a bit (try either with "Caecilia Regular" or "serif" as the family name). Using a custom version of it will probably lead to inconsistent results, so I also wouldn't recommend that at first (unless it's heavily modified to have a different family name, and I mean that in terms of metadata. Filenames are irrelevant here, and you in fact don't need to touch them in any way
).
You actually need the USE_ALT_FONTS stuff if you want to populate the Aa menu. But no matter, the hack handles that for you (i.e., you'll find that the file will have been recreated by the hack if you restart your device).