Eliot,
I think it is terribly unlikely that we wiuld ever find evidence for “the idea that some mutations are preplanned”.
As long as Christian Evolutionists include freewill in their views, there is no reason to assume that some changes are unplanned. In front-loading, EVERY change is intentional.
Finally, i think we can quickly dismiss the idea that frontloading implies that some fully-formed genes are like easter eggs buried in the genes of distant ancestors … just waiting to be activated in some future generation.
In a frontloaded scenario, all mutations would be planned.