For operations sake... provided you didn't send a denial once they were turned down for initial secondary market prodcut... you would be easier served to go with a counter-offer, which counts as a denial... unless they accept the counter-offer. I believe you are able to redisclose the GFE because of the product change, but only the elements of the GFE which change as a direct result of the product change.
However, if you already provided an AAN (a clear denial), you would have to, in my opinion, get a new application and start over. You can choose to use the same information but be careful of using the same credit score for FCRA issue and the same flood cert where rules my apply.
Hope that opinion helps.
In life, there is a lot less that could get better and a lot more that could get worse.
MBA Fin/MBS HR
My views only!