This command allows some sky manipulation.

A video tutorial for this command is also available:
https://youtu.be/72enNR9rosc

Only Counter-Strike 2 is supported.

mirv_sky color <iR> <iG> <iB> <iA> | default - Set color override. RGBA format, values from 0 to 255.
mirv_sky material <sRelativePathToFile> | default - Set skybox material. It has to be re-applied if map changes.
mirv_sky clouds color <iR> <iG> <iB> | default - Set color override. RGB format, values from 0 to 255. It has to be re-applied if map changes.
mirv_sky clouds draw 0|1 - Enable (1) / disable (0) drawing of clouds.

For mirv_sky material command you would have to provide a relative path to an appropriate .vmat_c file.

Using Source2Viewer, open pak01_dir.vpk in game/csgo folder and find some in materials/skybox. Then right-click and press "Copy file path in package". You should get something like this: materials/skybox/cs_italy_s2_skybox_2.vmat_c. Then in-game do mirv_sky material "materials/skybox/cs_italy_s2_skybox_2.vmat_c"

You can create your custom material using CS2 Workshop Tools.

First you would need to create an addon in tools launch menu.
This would automatically create an addon folder, which you can find at path-to-cs2\content\csgo_addons\YOUR_ADDON_NAME.
Then in that folder create a materials folder and drop your HDRI environment map texture there. For the texture you can use any image with 2:1 aspect ratio.

In workshop tools open the material editor and create a new material using a sky shader. Save the material to the same folder as your texture.
Then you can select your texture in the material editor and save again. Workshop tools should automatically compile it.
You can find compiled files in path-to-cs2\game\csgo_addons\YOUR_ADDON_NAME\materials.

In path-to-HLAE\resources\AfxHookSource2 create a cs2 folder and then a materials sub-folder.
So you would have path-to-HLAE\resources\AfxHookSource2\cs2\materials. Copy and paste the compiled files there.
Then in-game you can reference them like this: mirv_sky "materials/my_cool_material.vmat_c"