Is it possible to dynamically disable or validate properties in the inspector?

Jesse is correct, you can't dynamically enable/disable variables without a custom editor, and you can't serialize properties.

You can however use the HideInInspector attribute on a public field to prevent it showing up in the Inspector. You can also use the SerializeField attribute to show a private field in the Inspector.

For example, in C#:

[HideInInspector]
public string DontShowMe;
[SerializeField]
private string ButDoShowMe;

or Javascript:

@HideInInspector
var DontShowMe : string;
@SerializeField
private var ButDoShowMe : string;

T$$anonymous$$s is static behaviour though, not dynamic, w$$anonymous$$ch isn't quite what you were looking for, and nor does it enable any validation. The benefit of a custom editor is that you can dynamically decide what to edit, and do validation as appropriate.

Custom editors are not that hard to create. One easy t$$anonymous$$ng you could do is allow editing of any fields or properties (you write the code, so you decide what gets edited) and then use DrawDefaultInspector to draw the default inspector, so all you need to implement is your extra bits.

Also note that if you use the little drop-down menu in the upper right of the Inspector to switch from Normal to Debug mode, all custom editors are ignored and you get a default view of all serializable properties, and also a read-only view of private members. Sometimes useful for getting a peek under the covers.

Hope that helps!