Yes, you can change your contact e-mail address anytime.
Log in to myCloud.ch with your Swisscom Login and password.
Click on your initials in the upper right corner and select "Settings" from the dropdown menu:
Click on "Change" under "Contact email":
Under "Availability via mobile phone and e-mail" click on "Change".
Adjust the mail address according to your wishes and click on "Save".
The email will be adjusted as soon as you log in to myCloud again.