Manage your Unity3D symbols easily within the Editor by defining menu items

CustomDefines.cs

using UnityEngine;
using UnityEditor;

public class CustomDefines {

	[MenuItem("Global Defines/My Symbol/Enable")]
	public static void EnableDebug(){
		Debug.LogWarning("Enabling MY_SYMBOL");
		var defines = PlayerSettings.GetScriptingDefineSymbolsForGroup(EditorUserBuildSettings.selectedBuildTargetGroup);
		string newDefine = "MY_SYMBOL";
		if(!defines.Contains(newDefine)){
			defines= string.Format("{0},{1}", defines, newDefine);
			PlayerSettings.SetScriptingDefineSymbolsForGroup(EditorUserBuildSettings.selectedBuildTargetGroup, defines);
			AssetDatabase.SaveAssets();
		}
	}
	
	[MenuItem("Global Defines/My Symbol/Enable", true)]
	public static bool EnableDebugEval(){
        #if !MY_SYMBOL
        return true;
		#else
		return false;
		#endif
	}
	
	[MenuItem("Global Defines/My Symbol/Disable")]
	public static void DisableDebug(){
		Debug.LogWarning("Disabling MY_SYMBOL");
		var defines = PlayerSettings.GetScriptingDefineSymbolsForGroup(EditorUserBuildSettings.selectedBuildTargetGroup);
		string newDefine = "MY_SYMBOL";
		if(defines.Contains(newDefine)){
			defines = defines.Replace(newDefine, "");
			PlayerSettings.SetScriptingDefineSymbolsForGroup(EditorUserBuildSettings.selectedBuildTargetGroup, defines);
			AssetDatabase.SaveAssets();
		}
	}

	[MenuItem("Global Defines/My Symbol/Disable", true)]
	public static bool DisableDebugEval(){
        #if MY_SYMBOL
		return true;
        #else
        return false;
		#endif
	}
}