\starttext

\startluacode
    fonts.handlers.otf.addfeature {
        name = "oneb",
        type = "substitution",
        data = {
            ["one"] = "one.ss01",
        }
    }
\stopluacode

% context

\definefontfeature[default-oneb][default][oneb=yes]
\definefontfeature[default-ss01][default][ss01=yes]

\definedfont[name:vollkorn*default]      123\par
\definedfont[name:vollkorn*default-oneb] 123\par
\definedfont[name:vollkorn*default-ss01] 123\par

% non context

\font\foo=name:vollkorn:mode=node;kern=yes;liga=yes;          \foo 123\par
\font\foo=name:vollkorn:mode=node;kern=yes;liga=yes;oneb=yes; \foo 123\par

\stoptext
