sure you can use = or + via lua.
function keyboard(eventType, character, keycode, modifiers)
if eventType == eEvtKeyUp then -- key released
if character == "r" then ... end
elseif eEvtKeyTextInput then -- special keys (down/hold)
if character == "+" then ... end
if character == "-" then ... end
end
return false
end
registerEventHandler("keyEvent", "keyboard")
... the only problem was that + key only works on keydown/hold & not key released for some reason. - works for either. keytextinput & keydown will continuously trigger every loop/frame until you release the key. I prefer to always use key released where possible. Also I'm not sure if arrow keys can be accessed via lua or not but you can access more keys than you can via the editor key actions.
Here is a list of key events, codes & modifiers that David provided me with...
// key events
eEvtKeyUp
eEvtKeyDown
eEvtKeyTextInput
// key modifiers
eKeyModLShift
eKeyModRShift
eKeyModLCtrl
eKeyModRCtrl
eKeyModLAlt
eKeyModRAlt
eKeyModLGui
eKeyModRGui
eKeyModNum
eKeyModCaps
eKeyModMode
eKeyModCtrl
eKeyModShift
eKeyModAlt
eKeyModGui
// key codes
eKeyReturn
eKeyEscape
eKeyBackspace
eKeyTab
eKeySpace