The elatin IM is good, but it has some weird conflicts, like ~s, which can be the Turkish s with a tail or §. For some reason, uim always gives the second (without giving a choice of which to use like e.g. ipa-x-sampa does). I've tried putting a modified version of elatin-rules in ~/.local/share/uim, but it still uses the one in /usr/share/uim. Do I have to move my modified version to /usr/share/uim (which isn't a safe thing to do)?

The customs directory also doesn't work, because it seems to just be used for a limited number of settings, not a way to modify the rules.