This would actually be preferable to how DNA seems to evolve. In most systems, there's actually quite an acute constraint to genome length due to the Error Threshold; when a genome gets too large, it has too many mutations and therefore the 'fittest' genome, often called the 'master' genome, cannot be sustained in the population. Therefore, there's quite a lot of evolution where the genome becomes essentially minified. Most often, this is done by overlapping genes on the DNA, (mostly by shifting the reading frame by one or two nucleotides for one of the two genes).
Fixing our inverted retina would be one of the low hanging fruits:
>The vertebrate retina is inverted in the sense that the light sensing cells are in back of the retina, so that light has to pass through layers of neurons and capillaries before it reaches the rods and cones. In contrast, in the cephalopod retina the photoreceptors are in front, with processing neurons and capillaries behind them. Because of this, cephalopods do not have a blind spot.
Genetic code in large, multicellular organisms is quite different; in mammals, for certain functions you have multiple pathways to achieve similar things through different vehicles (proteins). In this sense, it is more akin to building or blowing up a bridge in relation to a transportation network; usually, other paths still exist, but sometimes and in certain critical locations it really fucks up the infrastructure.
The trouble here is that we can't see those consequences until they end up hurting someone.