imessage with two phone numbers

Hi guys

I'm switching phone numbers soon on my iPhone and was wondering if there is a way for me to keep getting iMessages on my old number after the switch. Ideally I'd like to get those on my phone but could also be with my Mac which currently receives the messages going to my phone number.

What happens when you register a new phone number with your iCloud account ? Does the old number get removed, or does the old number get removed after a while automatically ?

Thanks for the help