Don't care what you do with it, just don't sell and Skyrim belongs to Bethesda, so keep that in mind.
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Changelogs
Version 1
Added LOD flags where needed.
Reverted asset paths on some STAT records.
File released as standalone for ease of management. Apparently it isn't really a fix, at least in current SMIM version, and more of a contingency in case you've installed merged plugin and don't have special snow cliffs (folder 75). Don't ask me how that can happen, I know only about my Skyrim's bugs. If plugin makes more harm than good I'll just delete the whole page.
Here is a bit of a creative reenactment of what caused the existence of this patch:
Entering Haemar's Cavern (cell name: HaemarsShame01), going down the ramp, past the table and up the other ramp and forward just a bit before... CLANK!
Looking up it looks like I'm now in a pretty deep hole with a bunch of chairs, chests, dressers and a table above me... Reloading save confirms one thing - issue is persistent. xEdit shows that cell and the thing, that should've been where the hole is, aren't edited, CK shows that "the thing" is a cliff, loading CK with all plugins even remotely editing cell proves that indeed there is a cliff.
Maybe a mesh issue? Cliff FormID is 0004a71c, going back to xEdit only one plugin edits this STAT: SMIM-SE-Merged-All.esp
Path to mesh asset is set as "dungeons\caves\green\cliffs\SMIMICE\cavegcliffs03ns-SMIMICE.nif" which, is not in BSA with installed files and core files (necessary assets are actually in folder 75, easy to miss I guess). Reverting paths to vanilla brings back pretty nice cliff.
Cause of the issue: (potential) user error. Case closed, use plugin with caution.