Changing original frame for a custom one - can I keep old UK reg?

Afternoon Guys, I have started a project (non Rocket) which includes replacing the original frame with a new, custom built one in a different style (hard tail) I still have the original frame with the VIN on the V5, and the new frame has it's own number. So my question is, how do I go about transferring the old reg onto the new frame? I really hate the idea of having to get a Q plate, and ideally want to put my personal plate on it at some point so are there any tips I need to know to make this possible?
As always, any help & advice is appreciated - there is a lot of knowledge on here

I’m stateside, so my information may not be applicable. But here in my state, as long as you keep the headstock that has the Vin number etched into it, then yes, you can keep the same registration.

Bit of a conundrum - you can replace chassis on a landrover and retain reg number, you can even replace bulkhead. I would ( thinking aloud) think that new frame would equal different bike, therefore rendering it a " kit" vehicle hence q plate. Hope I'm wrong and I'm sure someone will correct me. All the best...

After some extensive research on the forums it appears that as long as you keep the original headstock (with VIN) the rest of the frame can be modified to your hearts content! So in theory you can weld the original headstock onto anything you like with no changes to the paperwork at all. Sounds ridiculous but you could legally weld a Honda 125 onto a Honda Goldwing and still call it a 125 with a different engine!