I’ve just got a new front door and in fitting it, the mains powered doorbell had to be disconnected. At the moment I have 2 wires inside the house that activate the original doorbell when connected. I was wondering how hard it would be to adapt a wireless doorbell into just a wireless activated switch that could operate my original doorbell from outside. I am guessing it is possible as I only need half of the circuit of a wireless doorbell but is it a practical possibility? Thanks in advance

Yes, quite possible.
However, in the real world, it wouldnt be practical.
The outside bell push is just a transmitter, the bell box inside is the receiver. So, if you wanted to use the old bell box still, you’d have to connect up the old bell box, and the new bell box /receiver, and have a relay or something similar to do the switching to ring the old bell.

Why not just drill a hole through a suitable point, re-route the cable and re-fit the old bell push?

Sounds like your trying to use the worst part of both systems. As above I’d refit the old bell push or fit a complete new wireless system. Wired systems are my preference.

I liked my old doorbell sound basically. And it is a terraced house where the new door frame stretches as wide as it can go meaning that there isn’t any room any more for a hole to be drilled to outside. I’m not worried about using the old bell push, just would prefer to have my old bell sound. So if I could have a wireless system that rather than makes a new bell sound connects my old one, it would be great, otherwise I’ll have to just go to a tacky wireless one

Doorbells are for houses with net curtains.

Get a knocker. A big fat brass one.

The knocker on the new door is stylish
…and pathetic and close to useless