Unity3D script to rotate the skybox

Skybox-6Sided-Rotated.shader

// Upgrade NOTE: replaced 'mul(UNITY_MATRIX_MVP,*)' with 'UnityObjectToClipPos(*)'

Shader "Skybox/6 Sided-Rotated" {
Properties {
	_Tint ("Tint Color", Color) = (.5, .5, .5, .5)
	[Gamma] _Exposure ("Exposure", Range(0, 8)) = 1.0
	[NoScaleOffset] _FrontTex ("Front [+Z]   (HDR)", 2D) = "grey" {}
	[NoScaleOffset] _BackTex ("Back [-Z]   (HDR)", 2D) = "grey" {}
	[NoScaleOffset] _LeftTex ("Left [+X]   (HDR)", 2D) = "grey" {}
	[NoScaleOffset] _RightTex ("Right [-X]   (HDR)", 2D) = "grey" {}
	[NoScaleOffset] _UpTex ("Up [+Y]   (HDR)", 2D) = "grey" {}
	[NoScaleOffset] _DownTex ("Down [-Y]   (HDR)", 2D) = "grey" {}
}

SubShader {
	Tags { "Queue"="Background" "RenderType"="Background" "PreviewType"="Skybox" }
	Cull Off ZWrite Off
	
	CGINCLUDE
	#include "UnityCG.cginc"

	half4 _Tint;
	half _Exposure;
	uniform float4x4 _Rotation;

	float4 RotateAroundYInDegrees (float4 vertex, float degrees)
	{
		float alpha = degrees * UNITY_PI / 180.0;
		float sina, cosa;
		sincos(alpha, sina, cosa);
		float2x2 m = float2x2(cosa, -sina, sina, cosa);
		return float4(mul(m, vertex.xz), vertex.yw).xzyw;
	}
	
	struct appdata_t {
		float4 vertex : POSITION;
		float2 texcoord : TEXCOORD0;
	};
	struct v2f {
		float4 vertex : SV_POSITION;
		float2 texcoord : TEXCOORD0;
	};
	v2f vert (appdata_t v)
	{
		v2f o;
		o.vertex = UnityObjectToClipPos(mul(v.vertex, _Rotation));
		o.texcoord = v.texcoord;
		return o;
	}
	half4 skybox_frag (v2f i, sampler2D smp, half4 smpDecode)
	{
		half4 tex = tex2D (smp, i.texcoord);
		half3 c = DecodeHDR (tex, smpDecode);
		c = c * _Tint.rgb * unity_ColorSpaceDouble.rgb;
		c *= _Exposure;
		return half4(c, 1);
	}
	ENDCG
	
	Pass {
		CGPROGRAM
		#pragma vertex vert
		#pragma fragment frag
		sampler2D _FrontTex;
		half4 _FrontTex_HDR;
		half4 frag (v2f i) : SV_Target { return skybox_frag(i,_FrontTex, _FrontTex_HDR); }
		ENDCG 
	}
	Pass{
		CGPROGRAM
		#pragma vertex vert
		#pragma fragment frag
		sampler2D _BackTex;
		half4 _BackTex_HDR;
		half4 frag (v2f i) : SV_Target { return skybox_frag(i,_BackTex, _BackTex_HDR); }
		ENDCG 
	}
	Pass{
		CGPROGRAM
		#pragma vertex vert
		#pragma fragment frag
		sampler2D _LeftTex;
		half4 _LeftTex_HDR;
		half4 frag (v2f i) : SV_Target { return skybox_frag(i,_LeftTex, _LeftTex_HDR); }
		ENDCG
	}
	Pass{
		CGPROGRAM
		#pragma vertex vert
		#pragma fragment frag
		sampler2D _RightTex;
		half4 _RightTex_HDR;
		half4 frag (v2f i) : SV_Target { return skybox_frag(i,_RightTex, _RightTex_HDR); }
		ENDCG
	}	
	Pass{
		CGPROGRAM
		#pragma vertex vert
		#pragma fragment frag
		sampler2D _UpTex;
		half4 _UpTex_HDR;
		half4 frag (v2f i) : SV_Target { return skybox_frag(i,_UpTex, _UpTex_HDR); }
		ENDCG
	}	
	Pass{
		CGPROGRAM
		#pragma vertex vert
		#pragma fragment frag
		sampler2D _DownTex;
		half4 _DownTex_HDR;
		half4 frag (v2f i) : SV_Target { return skybox_frag(i,_DownTex, _DownTex_HDR); }
		ENDCG
	}
}
}

Skybox-Cubed-Rotated.shader

// Upgrade NOTE: replaced 'mul(UNITY_MATRIX_MVP,*)' with 'UnityObjectToClipPos(*)'

Shader "Skybox/Cubemap-Rotated" {
Properties {
	_Tint ("Tint Color", Color) = (.5, .5, .5, .5)
	[Gamma] _Exposure ("Exposure", Range(0, 8)) = 1.0
	[NoScaleOffset] _Tex ("Cubemap   (HDR)", Cube) = "grey" {}
}

SubShader {
	Tags { "Queue"="Background" "RenderType"="Background" "PreviewType"="Skybox" }
	Cull Off ZWrite Off

	Pass {
		
		CGPROGRAM
		#pragma vertex vert
		#pragma fragment frag

		#include "UnityCG.cginc"

		samplerCUBE _Tex;
		half4 _Tex_HDR;
		half4 _Tint;
		half _Exposure;
		uniform float4x4 _Rotation;

		float4 RotateAroundYInDegrees (float4 vertex, float degrees)
		{
			float alpha = degrees * UNITY_PI / 180.0;
			float sina, cosa;
			sincos(alpha, sina, cosa);
			float2x2 m = float2x2(cosa, -sina, sina, cosa);
			return float4(mul(m, vertex.xz), vertex.yw).xzyw;
		}
		
		struct appdata_t {
			float4 vertex : POSITION;
		};

		struct v2f {
			float4 vertex : SV_POSITION;
			float3 texcoord : TEXCOORD0;
		};

		v2f vert (appdata_t v)
		{
			v2f o;
			o.vertex = UnityObjectToClipPos(mul(v.vertex, _Rotation));
			o.texcoord = v.vertex.xyz;
			return o;
		}

		fixed4 frag (v2f i) : SV_Target
		{
			half4 tex = texCUBE (_Tex, i.texcoord);
			half3 c = DecodeHDR (tex, _Tex_HDR);
			c = c * _Tint.rgb * unity_ColorSpaceDouble.rgb;
			c *= _Exposure;
			return half4(c, 1);
		}
		ENDCG 
	}
} 	


Fallback Off

}

SkyBoxRotation.cs

using System.Collections;
using UnityEngine;

namespace UGS.environ {

	/// <summary>
	/// Rotates the skybox of the scene or camera.
	/// Requires a special shader.
	/// </summary>
	internal sealed class SkyBoxRotation : MonoBehaviour {

		[SerializeField]
		private string propertyName = "_Rotation";

		[SerializeField]
		private Vector3 eulerAngles = Vector3.zero;

		[SerializeField]
		private bool affectCameraOnGameObject = false;

		[SerializeField]
		private bool continuousUpdate = false;

		private Material skyBoxMaterial;

		public void Awake() {
			setup();
		}

		[ContextMenu("Re-setup")]
		private void setup() {
			skyBoxMaterial = getSkyboxMaterial();
		}

		public void Start() {
			applyRotation();
		}

		public void OnEnable() {
			if (continuousUpdate) {
				StartCoroutine(continuousUpdateCoroutine());
			}
		}

		public void OnDisable() {
			if (continuousUpdate) {
				StopAllCoroutines();
			}
		}

		private IEnumerator continuousUpdateCoroutine() {
			while (true) {
				applyRotation();
				yield return null;
			}
		}

		[ContextMenu("Apply skybox rotation.")]
		public void applyRotation(bool reacquireMaterial = false) {
			if (reacquireMaterial) {
				setup();
			}
			var rot = Quaternion.Euler(eulerAngles);
			var matrix = Matrix4x4.TRS(Vector3.zero, rot, new Vector3(1, 1, 1));
			skyBoxMaterial.SetMatrix(propertyName, matrix);
		}

		private Material getSkyboxMaterial() {
			if (affectCameraOnGameObject) {
				var skybox = GetComponent<Skybox>();
				Assert.IsNotNull(skybox);
				return skybox.material;
			} else {
				return RenderSettings.skybox;
			}
		}

	}
}