You might take a look at Bitlash, which you will find at at http://bitlash.net -- Bitlash is a serial interpreter which runs entirely on Arduino, and it supports "macros" which are stored sequences of operations.
Here is how you might define on and off for your requirements:
> startup:="pinmode(13,1)"
> on:="d13=1"
> off:="d13=0"
Then you can say:
> on
or
> off
And the pin D13 will turn on and off, controlling your LED.
Happy hacking,
-br