Series of minor questions about OpenPGP 1

[Peter Thomas]

Hi.

I've just made some tests. And it showed that anybody can change the
paket header from old to new for any key (even without the secret
key).
Of course I've expected this, but is this the case for all signature
types, that gnupg doesn't include the paket header in the signing but
just the body?

Thanks,
Peter.