Transponder Programming: WFS 3 Key Learning

Hello,
I would like to have a key made for a VW Polo (year 2000) and then program it using VAG-Com. The vehicle already has the third-generation immobilizer. Since replacement keys from VW are relatively expensive, I've come up with the following idea: The transponder is only inserted into the key with the light. You can purchase a cheaper key with the transponders for the third-generation immobilizer from various online auction sites. The shape of the key can be replicated using a standard blank. Then, the transponder is attached to the replicated key.
Okay, now let's get to the main issue: To program the key, I need the numbers from the VW dealer. Are these numbers transponder-specific, or can I use a valid number to program any transponder to the car?

Thank you in advance for your efforts.
Matthias Hugel.