I am trying to create an override for a JSON store, but it is not behaving as I would expect -- none of my values seem to have taken effect. Why the need for an override of the store in the first place, you ask? A few reasons:
1) Set custom headers to include some authorization information
2) Change the read method to POST instead of default of GET
3) Remove extra parameters being included by default on the URL (page, start, limit, and cache-busting variable)

For #3, you can theoretically change to "undefined" the values of pageParam, startParam, and limitParam in SA to have them not included in the URL. In my experience, this mostly worked. If you were only trying to remove one of them, it would work just fine, but when removing all of them, it left the last one as actually named "undefined" instead of not including it. Appears to be a bug to me.

When launching the code in the web browser, it looks like the Store that is being used is the generated class rather than my overridden class. Is this because the StoreManager is getting the generated one instead of the overriden one? My application entry point (app.js) does correctly display the Ext.application as requiring Cars.store.override.TestStore.

Below is an example of what my override looked like after creating it in SA. A variant works properly when hand-editing Cars.store.TestStore, but that is obviously against the principles of using Sencha Architect. I'm sure they'll be a natural way to do this in SA eventually without the need for an override in the future, but there doesn't appear to be a way currently.

Code:
Ext.define('Cars.store.override.TestStore', {
    requires: 'Cars.store.TestStore'
}, function() {
    Ext.override(Cars.store.TestStore, {
        
    extend: 'Ext.data.Store',
    requires: [
        'Cars.model.CarData'
    ],
    constructor: function(cfg) {
        var me = this;
        cfg = cfg || {};
        me.callParent([Ext.apply({
            autoLoad: true,
            storeId: 'TestStore',
            model: 'Cars.model.CarData',
            proxy: {
                type: 'ajax',
                noCache: false,
                pageParam: '',
                startParam: '',
                limitParam: '',
                url: 'http://localhost/cars/getAllCars',
                actionMethods: {
                    read: 'POST'
                },
                headers: {
                    'Content-Type':'application/json; charset=utf-8',
                    'Authorization': 'Basic ' + Base64.encode('username:password')
                },
                params : Ext.JSON.encode(''),
                reader: {
                    type: 'json',
                    root: 'data'
                }
            }
        }, cfg)]);
    }
    });
});