Note 1:
The instructions herein are made obsolete by the addition of support for Respackopts.
Download from https://modrinth.com/mod/respackopts and use the gizmo in the resource pack selection screen.
(you can still you the manual method described below, if you really want to)

Note 2:
If you're using Celestial 2.0 to use the pack, you may still use the manual method below, as with Respackopts,
the in-game chat will spew out errors from Celestial if you disable any features. This does not break the
pack in any way, it will still work perfectly fine, but in case that bothers you, do it manually.
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Nuit:
Overworld sky directory: assets\nuit\sky\overworld\
End sky directory: assets\nuit\sky\the_end\
Delete the json file for the corresponding feature that you wish to remove.

Celestial:
Overworld sky: assets\celestial\sky\overworld\sky.json
End sky: assets\celestial\sky\the_end\sky.json
Nether sky: assets\celestial\sky\the_nether\sky.json
Open the json file, and delete the full quoted line along with the comma from "sky_objects", that you wish to remove.
(Make sure each sky object remains separated by a comma, otherwise the file will break. The last line must not have a comma after it!)

Biome dependant clouds:	can not be easily removed
Rain clouds:		sky 027 and 280-289 and 433-436
Snow clouds:		sky 026 and 270-279 and 429-432
Lightning strikes: 	sky 303-314 and 324-325
High altitude clouds:	can not be easily removed
Rainbow: 		sky 268
Iridescent clouds:	sky 330-332
Noctilucent clouds:	sky 328-329
Asperitas clouds:	sky 322-323
Mammatus clouds:	sky 318-319
Fiery sunsets:		sky 326-327
Sandstorm:		sky 026 and 290-299 and 434-437
Tornadoes:		sky 315-317
Supercell:		sky 333-334
Solar eclipse:		sky 401-440 and 507
Blood Moon / Blue Moon:	sky 011-014
Gas giants:		sky 004-005 and 405-406
Auroras:		sky 301-302
Northern star:		can not be removed
Shooting stars:		sky 029-032
Meteor shower:		sky 033-035
Black hole:		sky 001 (distortion) and sky 003 and 404
Andromeda:		sky 002
Light pollution:	sky 006
Outer space:		sky 501-507
Hurricane:		sky 320-321 and 503
Main End sky:		sky 001
End highlands:		sky 002
End midlands:		sky 003
End barrens:		sky 004
Small End islands:	sky 005
End black hole:		sky 006-009 and 011-012
Red Nether sky:		sky 001
Cyan Nether sky:	sky 002
Brown Nether sky:	sky 003
High Nether sky:	sky 004