I don't think so.
But maybe check with 48 support to be sure.
See the link in my signature below or email them at email@example.com
I'm pretty sure that just porting a number in will not bump you off the old €7.99 membership, but you might want to check just to be 100% sure... 🙂
Judging by this, the only thing that would bump you off being able to buy the €7.99 membership would seem to be if you bought another membership at some point.