KA,
I'm not an expert on the 203k's, but I can tell you that it's not too late to switch, just need to get over some hurdles first. You'd need to re-do the purchase agreement and state that you're switching programs, which might make the sellers change their mind, since it's not as simple of a program as a regular FHA and could drag out the closing date. You'll also need to make sure you're working with a broker/lender who has experience with this type of program, as there is a lot more involved to the process. It's also an FHA product, so you'd still be held to the 5 year minimum for the MI.