I'm not sure you'd get a friendly response from anyone about that actually.
You might end up with some angrily placed smog-related stickers, though...
If you think it's a good idea, that's great... I don't think anyone else will agree, though.
Now, if you were able to sustain an average substantially higher than other drivers, or had done some real modding and made it obvious that you're at least making an attempt at it, or anything of the sort, it would probably be a different story... thankfully, you'll only have to deal with your intended PUN until next registration time, if you decide to go through with it.
Frankly (Frank Lee.. LOL) I think you should take it as a joke, what your G-pa most likely intended it to be, and leave it as that for now. It'll still be available next time around.