yes it's possible - you're looking here to do a partial reload. I'm not sure whether it is possible to schedule like this without using QlikView Publisher.
Anyway, when you do a partial reload, you can specify each of your loads as an ADD or REPLACE, which will allow for concatenation, or replacement of your tables respectively. If one of your tables exists from your full load and doesn't have an ADD or REPLACE associated with it, it will remain in your data model from your initial full load.
Also there's an IsPartialReload() function which will allow you to add some control structures to your reload acript.