Yes you can fly any single engine propeller aircraft (you've done differences training on) with a SEP NPPL - but just in UK airspace and you can't add things like a night rating or IMC. Question would be are you taking the NPPL (microlight) or the SEP NPPL?
You can 'update' your microlight NPPL with the SEP rating, tailwheel and complex types (varible pitch prop and retractable gear).
The C42 is, like many aircraft of the microlight type, an odd one. As far as I am aware you can't maintain your SEP NPPL rating or PPL licence on this type because of it's microlight clasification, however there are some versions out there on which you can.
Someone with a little more knowledge will provide a more expansive answer I'm sure. While you wait for the Guru to arrive
here is a link you may wish to follow which should answer more of your questions.