I am fairly new to the creation kit, but I have a lot of ideas I am hoping I could bring to life. One of those ideas is to make a rune spell, but instead of having it's normal effect when it explodes it explodes differently, say, an unrelenting force. Is this possible to modify a rune spell in such a way, if so, how would I go about doing it?

Yes it's possible. I don't have the creation kit under hand, but you want to copy a MGEF (for exemple the fire rune magic effect) and instead of a fire damage add the unrelenting force effect. I don't remember if the last one is a script effect, but this is the start.
you could also look here http://www.creationkit.com/Magic_Effect for other hints.

after you created the magic effect you use it creating a new SPEL. you want, maybe, to copy the fire rune one to see how it works. Sorry but now i can't be more detailed. But well, it's a start