You can simply use myStore.sync(), you don't need to specify id. The sync function will examine the store contents, and add/delete/update records as needed.

When using REST, you can set writeRecordId of Ext.data.write.Writer (see here) to false, since with REST id is usually appended to the URL, as in your case.

I solved by extending Ext.data.proxy.Rest and overriding the buildUrl method to be able to extract the ID from the request parameters. Then I used this overridden proxy in my model:

Ext.define('MYPROJ.proxy.Settings', {
   extend : 'Ext.data.proxy.Rest',
   alias  : 'proxy.settings',
   buildUrl(request) {
      const url = this.callParent([request]);
      const id  = request.getParams().id;

      if (id) {
         delete request.getParams().id;

         const proxyUrl = request.getProxy().getUrl();

         return url.replace(proxyUrl, `${proxyUrl}/${id}`);
      }

      return url;
   }
});

Ext.define('MYPROJ.model.Setting', {
   extend  : 'Ext.data.Model',
   alias   : 'model.setting',

   clientIdProperty: 'clientId',

   fields: [{
      name    : 'id',
      type    : 'int',
      persist : false
   }, {
      name   : 'name',
      type   : 'string',
      unique : true
   }],

   proxy: {
      type : 'settings', // <- Use overridden proxy here
      url  : `/something/settings`
   }
});

Then in my code I can use sync() like this:

const myID = 10;

this.settingsStore.load({id: myID});

//...

this.settingsStore.sync({params: {id: myID}});

When sync() is called myID will be extracted from params on MYPROJ.proxy.Settings and added to the URL (/something/settings/10).