[JensRex]

I did this just the other day. I left out about 20% of the normal wheat flour, and added some whole wheat flour. You can't substitute it 1:1, so experiment a little until the dough feels right.

I've made this recipe many times, but I go by another[1] method, which is less wall-of-texty, but basically the same.

[1] https://en.wikipedia.org/wiki/No-knead_bread

[saalweachter]

A good rule of thumb is "only replace some of the standard all purpose / bread flour". Swapping a cup or two out for oat or whole wheat or rye or whatever is usually fine; replacing it all tends to be trickier.