can Content-Type be set of the body of the message?

Hi,

For attachments, gnus prompt me for a content type (with a sensible
default), but when composing messages, can I set it explicitly? For
example (a bad one, though) if I wrote the email (actually pasted from
somewhere) with html markup tags, for example "<h1>Some Header</
h1><p>some text</p><p>some more</p>" can I explicitly say the content
type is text/html so that the receiving end renders correctly? Or if I
pasted some text which is already quoted-printable, e.g. have `=20'
etc inside, can I edit the content-type to add a transfer-encoding?

Thanks,
Kousik