It's only difficult if you don't know how to approach it. When ever I''m patching stucco after covering I take a 4" diamond blade grinder and run it along the edge to back cut a groove or two along the perimeter, this gives the patching material something extra to "Key" to. I already mentioned using the Milestone material to match in the underlying base coat. the next day you can use a power hand sander on the edges, I was using a small Makita with #60 grit sand paper. After it's sanded all you have to do is match in the textures, just constantly study the existing textures that you are matching.we have done these mexican, californian finishes in sand and cement here in england but i bet they are difficult to patch up!