I'm confused as to why you think that it's the April 15th deadline that will get you in trouble here. This deadline is in place as an attempt to prevent schools from forcing students to make an early decision. If you made an early decision of your own accord, and now wish to change that decision, this situation really has nothing to do with April 15th.
As TakeruK suggested, there are likely to be financial ramifications of changing this decision and it would very probably make people at that school look poorly on your professional behavior. However, I can imagine a few instances where it would be worth the risk.