Interesting reply. I'm not sure the iPhone actually channels eSIM activation packets through VPN (just like it doesn't send iMessage or Facetime through VPN). I've never tried to trace those packets so I can't say for sure, but it's worth a try I'd say. Just make sure you have a backup plan if it ends up not working.
Also, these things apply no matter if you're switching from physical SIM to eSIM, or swapping an eSIM to a new device: it's still a new eSIM activation as far as the operator is concerned (but customer care agents don't know that).
Source: I work for a mobile operator myself.