Existing customer activation fee, can I dispute a hasty agreement?

I have a question, I only just finished a live chat via the my virgin media app with a support agent to try to resolve a bug in my hub 4 ive suffered through for a while but finally got round to resolving by explaing the issue then requesting a replacement upgrade to a hub 5. The side reason was to get the recommended hub 5 for use with the 1gig service replacing the hub 4 that was rushed out to give to early adopters.

At first the agent wanted to send an engineer out to which I said why waste the money to send an engineer out for just a replacement hub then asked for it to be sent out as a self install which was agreed too. 

The self install and the hub 5 is on its way but I since been thinking, was I too hasty when I said yes to the activation fee of £35 (probably due to my elation at getting a working and suitable hub), granted I get why new customers pay the fee as its a completely new install and setup, but surely existing customers shouldn't need the fee if the only change is to be a simple mac address value change, (be nice if this too was self install via a web app, would no doubt save virgin media even more money too).

Well if love to hear thoughts and experiences, and maybe if I'm lucky a response from a virgin media employee. 

Thanks