I do not have Muscovies but I do teach high school genetics. So, I am not any expert but know enough to be dangerous. To answer your question, no, the way I understand it, genes don’t change from recessive to dominant. Two possibilities I can think of.
One, your drake actually does carry ripple. Recessive can hide for many generations (think red hair or blue eyes in people). If this is the case, I would have expected more rippled ducklings from your two hens. Half of them, from those hens according to my punnet square. Perhaps your two rippled hens are not contributing as many fertile eggs to the flock.
Two, new mutation. Most “new” varieties are recessive because they are just broken recipes or mutations. Let’s say a certain gene is the recipe for a protein whose job is to put color in a feather. The gene gets copied wrong so the protein doesn’t work and no color is put in the feathers, so white. Since all animals have two copies of each gene (called alleles) it would take getting a broken recipe from both parents, or two recessive alleles to be a white duck. All this to say if ripple works in a similar way, your two rippled ducklings could have inherited one rippled allele from their mothers but the second allele could be from a new mutation from the drake.
. The first explanation makes more sense to me because you got two rippled ducklings.
