The Issue:

As Lighting, Fog, Ambient Music, Weather, and Location are all contained in the CELL records, Mods that modify these can (will) cause Previs issues in your load order.

The safest way to handle such Mods is by placing them BEFORE (above) Previs mods (such as PRP), however this disables their intended changes as well.

My FO4CheckPrevisbines.esp xEdit script can solve this. Simply place ALL your mods that modify Lighting, Fog, etc before PRP, then run my script either against PRP.esp, or your entire load order, choose the "Create Patch to only fix wrong Regions/MHDT/LCN/EDID/etc (from conflicts)", Change the Patch name to something suitable, and click "OK".

The resulting Patch should be placed towards the end of your load order (after any of your Previs Mods), and will have brought forward all the changes to lighting, weather, etc that were overriden by later Mods - while keeping all the Precombine information intact.

I have sucessfully used this to create patches just like you find in the PRP updates download for Clarity etc.

What it does:

It looks for the last change (override), of the particular CELL fields, that does not revert the field back to Base Game settings (and is not blank).
This is merged with the winning CELL override (containing the current Previs data) into the Patch.

So with a load order like:

Base Game, other mods, etc
Lighting Mod (changes lighting data in cell A)
PRP (adds Previs to Cell A, but resets lighting data back to Base Game values)
Previs Patches ('New' previs for Cell A, but also resets lighting data to Base Game)

The patch will contain the 'New' Previs Data, but the Lighting Data from the Lighting Mod.
Obviously if multiple mods make conflicting, new, changes then you may need to modify it to use the desired values.

Cell Values Checked:

Currently the following fields CELL are checked/brought forward:

- 'MHDT' - Max Height Data (for flying vehicles)
- 'XCLR' - Regions (this is a cummulative list of all the regions in every override)
- 'EDID' - EditorID
- 'XCLL' - Lighting
- 'XLCN' - Location
- 'XCMO' - Music Type
- 'XEZN' - Encounter Zone
- 'XCAS' - Acoustic Space
- 'XCIM' - Image Space
- 'XGDR' - God Rays
- 'XCCM' - Sky/Weather
- 'XCWT' - Water
- 'XILW' - Exterior LOD
- 'LTMP' - Lighting Template
- And Cell Flags No LOD Water, Show Sky, Use Sky Lighting, Distance LOD only, Has Water.

The following WRLD fields are also checked/forwarded:

- 'MHDT' - Max Height Data (for flying vehicles)
- 'MNAM' - Map Data
- 'XEZN' - Encounter Zone
- 'CNAM' - Climate
- 'LTMP' - Lighting Template
- 'XLCN' - Location
- 'NAM2' - Water
- 'NAM3' - LOD Water Type
- 'ZNAM' - Music


Note that you need the latest version of FO4Check_Previsbines.pas (V4.5).