My understanding is that accounts with "No P2P access" get assigned IP addresses in a particular range and that those IP addresses are blocked from establishing connections using ports known to be employed by P2P applications:
What services are not supported by ADSL Home Surf?[/url], Force9"]Software programs not supported include, but are not limited to, KaZaA, Gnutella, Edonkey, Napster, WinMX, Aimster and Audiogalaxy. To ensure the quality of service offered through Home Surf, all further file-sharing applications that become available will similarly not be supported.
It follows that if you change your account type from one with P2P restrictions to one with no restrictions (or vice versa), then the IP Address assigned to you will also change.