InfoPath Dev

Without any third party tools, without any custom code can one use a standard rule to change a combobox into a textbox.

I realize that the standard way to do this would be to have two sections that show conditionally and house the different two control types, both tied to the same data source. Any *easier* way to do this?

Using conditional formatting is essentially the only way to accomplish this, though I believe that it's fairlly easy. Note that you don't have to put the controls into sections. You can place the conditional formatting on the controls themselves.