Doesn't look like that did anything. Not quite knowing what you meant by "allow it to overwrite" I tried two things: installing it and putting it directly below Cathedral Landscapes in the load order (no change) and installing it and naming it Cathedral Landscapes, then merging the two (also no change). I saw a thread on the Cathedral subreddit where someone reported a similar graphical glitch, they seemed to fix it by setting bEnableProjecteUVDiffuseNormals=1 in the skyrimprefs ini, but when I looked there, it had already been set. So I'm stuck scratching my head here.