Custom classes vs writing Extensions

I could really use someone to verify my logic here.

I come from an IOS/Xcode/Objective C background

In most of my IOS/Xcode projects, for example, I have a class file called SteveTextField which extends Apple's UITextField. I use the SteveTextField class everywhere instead of a UITextField so that I can easily change global behavior for all of my text fields quickly and easily

Now I am trying to use Architect to build a complex ExtJS app. From what I've read so far, it seems I can't mimic this workflow and have it work visually in Architect. The only way it seems I can do this is to build an extension for architect to allow this type of functionality.

If I create a custom class in Architect that extends Ext.form.field.Text for example, it doesn't work in Architect's Canvas (Apple's Xcode environment sees the base class of a custom class and handles it nicely), it doesn't seem to be this way with the (current) version of Architect.

If I want to change some default config value for 20 field elements in an Architect app, it would seem that the only way to manage this type of thing is to build an extension?