KeyMap(keyFrom, keyTo)
example :

KeyMap(key_a, key_b);
on_a = function_a; // now pressing b will call function_a.


KeySwap(keyA, keyB)
example :

KeySwap(key_a, key_b);
on_a = function_a; // now pressing b will call function_a
on_b = function_b; // now pressing a will call function_b

Then, keyboard remapping will be more convenient.