I think you're overthinking this. It's as simple as changing the text within the quotes in the [submit] value. For instance, it looks like you would want to use [submit "Skicka"] in the form code area. You shouldn't have to dig around in any code.
Just click "Generate Tag", fill in whatever text you want to appear in the "Label" space, copy and paste that into the form area.
The easiest way, though, is simply to edit the quoted part within the default submit tag already in each new form. Where you see [submit "send"], change that to [submit "Skicka"].