preventing readonly fields and properties from being set

com.unity.perception/Documentation~/Randomization/Scenarios.md

 6. **OnComplete** - actions to complete after the scenario as completed
 
 ## Constants
-Scenarios define constants from which to expose global simulation behaviors like a starting iteration value or a total iteration count. Users can serialize these scenario constants to JSON, modify them in an external program, and finally reimport the JSON constants at runtime to configure their simulation even after their project has been built. Below is an example of the constants used in the `FixedFrameLengthScenario` class:
+Scenarios define constants from which to expose global simulation behaviors like a starting iteration value or a total iteration count. Users can serialize these scenario constants to JSON, modify them in an external program, and finally reimport the JSON constants at runtime to configure their simulation even after their project has been built. Below is an example of the constants used in the `FixedLengthScenario` class:
 ```
 [Serializable]
 public class Constants

com.unity.perception/Editor/Randomization/ParameterElement.cs

                 var fieldInfos = componentType.GetFields();
                 foreach (var fieldInfo in fieldInfos)
                 {
-                    if (fieldInfo.FieldType == propertyType)
+                    if (fieldInfo.FieldType == propertyType && fieldInfo.IsPublic && !fieldInfo.IsInitOnly)
                         options.Add(new ParameterTarget()
                         {
                             gameObject = obj,
                 var propertyInfos = componentType.GetProperties();
                 foreach (var propertyInfo in propertyInfos)
                 {
-                    if (propertyInfo.PropertyType == propertyType)
+                    if (propertyInfo.PropertyType == propertyType && propertyInfo.GetSetMethod() != null)
                         options.Add(new ParameterTarget()
                         {
                             gameObject = obj,