I did. I just repeated that again today.
Click on remove a host, select the only email address registered into spamcop.net. All two mailhost were deleted. The mailhost tab is empty with a link to register a mailhost.
Went through the process to register an email address. Selected the 2 MX host for the domain. Sent the configuration email. Processed the configuration email through spamcop.net. Both new MX host are registered.
But, the original mailhost that were originally register to the email still shows on the mailhost list. So now my email have 4 mailhost instead of 2.
I have no control of the older IP address, not sure if the will be used for spam or not.