Read all posts in the Stripy series. Ahem, sorry for the silly title. Anyway here's what I would do if I woke up one morning, found I had my breasts had grown a lot overnight, and decided to knit a well fitted stripy. Admittedly there might be some freaking out first because that would be one strange overnight growth spurt, but then, then I would decide I needed a new stripy. Of course.
This hasn't actually happened and I'm not really expecting it to (though if it did I would make a much better model for some of my rather hourglass shaped designs), so this remains hypothetical. Luckily for those of you who have less hypothetical boobs there's an awesome ravelry group The Bust Line where I found this helpful and interesting tutorial on adding both horizontal and vertical bust darts to sweater patterns (and she called it a tit-orial - clearly we are all 10!).
Seeing as I have no desire to re-write what is already covered there I'd advise you to read through it if you want to add extra shaping to Stripy. Once you've done that there are a few things I would suggest doing for this particular pattern.
The waist shaping is worked as a set of 6 paired decrease and increase vertical dart (2 at the sides and 2 each at the front and back), I'll cover that in my next post, so if you're adding extra boobage stitches at the front don't worry about how you're going to decrease them away, just make sure you have a note of the difference and you'll begin the front darts first and decrease the extra before continuing the rest of the waist shaping.
As the tutorial covers there are various ways to work the top vertical bust darts, but there is another possibility in this case. If you don't want the visual line of the dart, but do want the extra stitches at the front you can add them to the front raglan increases. Just work out how many extra stitches you want at each side and add that to your basic increase number. Then space this total number out over the raglan diagonal. You'll work the rest of the raglan in the same way, but increase more frequently at the two front 'seams'. I would add these increases only in the middle portion of the raglan 'seam' to get the extra stitches where you actually want them.
Horizontal darts worked using short rows and the spiralling stripes are really not going to play well together, it would be possible to work out but rather pointless since you probably don't want horizontal stripes cutting your boobs in half anyway. I think it would be much more flattering to continue with the single colour until you've completed the horizontal darts.