Can't change hotkey to toggle Surfingkeys

[julpec]

I tried to change the hotkey mapping like described here but it doesn't work. I would like to use <Alt-s> for another action (go one tab right), so I used this sequence :

api.unmap("<Alt-s>");
api.map("<Alt-s>", "R");
api.map("<Alt-i>", "E");

It works well but I lose the hotkey function.