Beginner question: how do I set the strength of a cube map reflection (pic+code)

Hello. I asked other questions about this shader in another thread, but since this is a new problem, here's another one. I'm a complete beginner when it comes to shaders.

I'm doing my own shader in Strumpy's Shader Editor, with minor tweaks by hand, and it works well enough. Now I've added a cube map reflection to my shader and I can't figure out how to control the strength of the reflection. It's either full chrome or nothing. How do I control the reflection with either a slider, a color or an alpha (or some other way)? It doesn't really matter how. Any tips appreciated!

Code (csharp):

1.  
2. Shader "WhiteLightmapAlphaReflections"
3. {
4.     Properties
5.     {
6. _SamplerCube("_SamplerCube", Cube) = "" {}
7. _Diffuse("_Diffuse", 2D) = "white" {}
8. _Lightmap("_Lightmap", 2D) = "white" {}
9. _GlossOchSpecferg("_GlossOchSpecferg", Color) = (0.1716418,0.1716418,0.1716418,1)
10. _Specular("_Specular", Range(0,1) ) = 0.75
11. _Clip("_Clip", 2D) = "white" {}
12.  
13.     }
14.    
15.     SubShader
16.     {
17.         Tags
18.         {
19. "Queue"="Transparent+100"
20. "IgnoreProjector"="False"
21. "RenderType"="Transparent"
22.  
23.         }
24.  
25.                     Pass {ColorMask 0}
26. Cull Back
27. ZWrite On
28. ZTest LEqual
29.  
30.  
31.         CGPROGRAM
32. #pragma surface surf BlinnPhongEditor alpha vertex:vert
33. #pragma target 3.0
34.  
35.  
36. samplerCUBE _SamplerCube;
37. sampler2D _Diffuse;
38. sampler2D _Lightmap;
39. float4 _GlossOchSpecferg;
40. float _Specular;
41. sampler2D _Clip;
42.  
43.             struct EditorSurfaceOutput {
44.                 half3 Albedo;
45.                 half3 Normal;
46.                 half3 Emission;
47.                 half3 Gloss;
48.                 half Specular;
49.                 half Alpha;
50.             };
51.            
52.             inline half4 LightingBlinnPhongEditor_PrePass (EditorSurfaceOutput s, half4 light)
53.             {
54. half3 spec = light.a * s.Gloss;
55. half4 c;
56. c.rgb = (s.Albedo * light.rgb + light.rgb * spec);
57. c.a = s.Alpha + Luminance(spec);
58. return c;
59.  
60.             }
61.  
62.             inline half4 LightingBlinnPhongEditor (EditorSurfaceOutput s, half3 lightDir, half3 viewDir, half atten)
63.             {
64.                 viewDir = normalize(viewDir);
65.                 half3 h = normalize (lightDir + viewDir);
66.                
67.                 half diff = max (0, dot (s.Normal, lightDir));
68.                
69.                 float nh = max (0, dot (s.Normal, h));
70.                 float3 spec = pow (nh, s.Specular*128.0) * s.Gloss;
71.                
72.                 half4 res;
73.                 res.rgb = _LightColor0.rgb * (diff * atten * 2.0);
74.                 res.w = spec * Luminance (_LightColor0.rgb);
75.  
76.                 return LightingBlinnPhongEditor_PrePass( s, res );
77.             }
78.            
79.             struct Input {
80.                 float3 simpleWorldRefl;
81. float4 meshUV;
82.  
83.             };
84.  
85.  
86.             void vert (inout appdata_full v, out Input o) {
87. float4 VertexOutputMaster0_0_NoInput = float4(0,0,0,0);
88. float4 VertexOutputMaster0_1_NoInput = float4(0,0,0,0);
89. float4 VertexOutputMaster0_2_NoInput = float4(0,0,0,0);
90. float4 VertexOutputMaster0_3_NoInput = float4(0,0,0,0);
91.  
92. o.simpleWorldRefl = -reflect( normalize(WorldSpaceViewDir(v.vertex)), normalize(mul((float3x3)_Object2World, SCALED_NORMAL)));
93. o.meshUV.xy = v.texcoord.xy;
94. o.meshUV.zw = v.texcoord1.xy;
95.  
96.             }
97.            
98.  
99.             void surf (Input IN, inout EditorSurfaceOutput o) {
100.                 o.Albedo = 0.0;
101.                 o.Normal = float3(0.0,0.0,1.0);
102.                 o.Emission = 0.0;
103.                 o.Gloss = 0.0;
104.                 o.Specular = 0.0;
105.                 o.Alpha = 1.0;
106. float4 TexCUBE0=texCUBE(_SamplerCube,float4( IN.simpleWorldRefl, 1.0));
107. float4 Tex2D1=tex2D(_Diffuse,(IN.meshUV.xyxy).xy);
108. float4 Tex2D3=tex2D(_Lightmap,(IN.meshUV.xyxy).xy);
109. float4 Multiply0=Tex2D1 * Tex2D3;
110. float4 Multiply1=TexCUBE0 * Multiply0;
111. float4 Tex2D2=tex2D(_Clip,(IN.meshUV.zwzw).xy);
112. float4 Master0_0_NoInput = float4(0,0,0,0);
113. float4 Master0_1_NoInput = float4(0,0,1,1);
114. float4 Master0_6_NoInput = float4(1,1,1,1);
115. o.Emission = Multiply1;
116. o.Specular = _GlossOchSpecferg;
117. o.Gloss = _Specular.xxxx;
118. o.Alpha = float4( Tex2D2.a);
119.  
120.             }
121.         ENDCG
122.     }
123.     Fallback "Diffuse"
124. }
125.