Callback when custom property attribute changes

I have a custom PropertyAttribute that looks like this:

```
using UnityEditor;
using UnityEngine;
using System;

public class StringInList : PropertyAttribute {
public delegate string[] GetStringList();

public StringInList(params string [] list) {
List = list;
}

public string[] List {
get;
private set;
}
}```

I have a custom struct MyStruct (not a monobehavior) that uses this StringInList property as a field. In the editor, this looks like a dropdown with a number of string choices.

What I'd like to do is change another field on MyStruct when my StringInList property changes. What's the right way to do this?
One option is to give the monobehavior that references MyStruct an OnValidate method, check for when this value on MyStruct changes, and update MyStruct accordingly, but that feels bad; I'd prefer to localize everything to MyStruct (or supporting custom editors/propertydrawers) if possible.