Hi Bethy, rye flour is a bit trickier than whole wheat flour to substitute for white flour because it doesn't develop gluten the same way wheat flour does, and won't benefit as much from the folding process. Recipes with a large percentage of rye flour also tend to require a somewhat different timeline, due to more rapid fermentation, so this could cause complications as well. I think it might work well to subsitute rye flour for the white flour called for in the preferment (so, use a total of  230g of rye flour in the preferment rather than 115g of rye and 115g of AP flour). I would also increase the liquid a bit in the preferment (227g) to adjust for the higher absorption of the rye flour. You could also try substituting 113g of whole wheat flour for a portion of the white flour called for in the recipe. This will likely give you a richer rye flavor and a little more sourness in the final loaf, and overall rise time might be a bit shorter. While your loaf will likely be a little moister and denser than the original miche, I would expect the end result will give you a more whole-grain option that is still a great loaf! If this plan sounds too ambitious, I think you could also simply substitute up to 1 cup (113g) rye flour for a portion of the white flour called for in the dough portion of the recipe, and this should work well without further revisions to the recipe. 

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