\startluacode
    fonts.handlers.otf.addfeature {
        name = "mojca",
        type = "multiple",
        prepend = true,
        data = {
            ["č"] = { 0x30C, "c" },
        }
    }
    fonts.handlers.otf.addfeature {
        name = "kern",
        type = "pair",
        data = {
            [0x30C] = { c = { { 500, 0, 0, 0 }, false } },
        }
    }
\stopluacode

\definefontfeature[default][default][mojca=yes]

\showframe

\starttext

    mojča miklave\utfchar{"30C}c

\stoptext
