Also note that DEO is popular enough (coming in #3 on the "List of spells someone in the covenant should know," https://forum.atlas-games.com/t/card-board-games-archive-links/116/1), it's probably pretty easy justify knowing an in-game version that has been Experimented or Breakthrough'd on.
So if you go this route, you can probably find a version that has Multiple, Silent, Penetrating, or Flexible casting built in (or whatever your troupe thinks is appropriate). Of course, it might also turn your skin green, make a horrible screeching noise, or make you smell like cheese for three days after casting, but them's the breaks for Phenomenal Cosmic Power...
Also, I would argue that the spell you described can currently be modeled as a general Muto Vim spell - changing nothing but the Realm of the effect would, IMO, be a "Medium" change. Which would be (game-mechanically) balanced out by the fact that you would have to make a Concentration roll in order to successfully cast. But honestly, this runs into the same issue that Jonathan brings up - it's probably easier (and safer) to just learn the 3 version separately. Because unless you designed your mage to be a Concentration specialist (ie, Cautious Concentration), you probably don't want to risk blowing that roll when the dragon's breathing down your neck.