The subform itself should be a form that is saved in the forms list anyway unless you dragged and dropped a table or query in Access 2007 or 2010 which then just puts the table or query on the form.
The subform CONTROL is such that you can just simply select a different Source Object from its SOURCE OBJECT property in the DATA TAB, if you select the subform control (the control on the parent form which houses the subform). You will have to change the Master/Child links too, if they are different from the other one.
So you don't have to "put another" subform on the form to do all of that.