1st IWC and a couple of questions about the watch

I have recently bought a portuguese chrono. The case is gold and
the top part is in white and I was curious if I could change the
top of it so that it can be black? Thank you for you help!!

Theoretically it's possible, but a change of dial even if original factory dial alters the model number. That is then not correct for the paperwork. The markers on the black dial are silver in colour and this dial is normally used in stainless steel cases. I'd leave well alone.

A warm welcome to our company.
Agree with Greg my friend, leave it as it is.
Congratulations for your new watch

Welcome to the Forum, may you get only good hours displayed!