Recommendation to spay at 6 months is pretty standard vet advice... I thought the OP was talking about very young pups...
I have to say, while there are arguments for and against spaying at 6 months, I really don't think coat change should be the motivating factor...
If we are talking about much younger pups, I still think it is a consideration of the health benefits/risks that should be the deciding factor, not losing the smooth puppy coat.