How to alter contact (e-mail)?

An Apple ID's "username" is a valid email address. You can change this address, as long as, it doesn't end with @icloud.com, @mac.com, or @me.com.

However, I'm not 100% sure that this will work in this case. Maybe someone else who tried this can chime in and let us know. The following Apple Support article seems to support the idea that you can:

What to do after you change your Apple ID email address or password - Apple Support

Clarification question - do want to change your Apple ID e-mail address or your user name for the discussions here? If your Apple ID e-mail address, see the link below. If your user name for the discussions here, clearly state that and someone can report it to the hosts who should contact you to make the change.

Apple ID Name Change

Sorry, but you can't retain your ASC discussions if you use a different ID. AFAIK, all of these discussions are associated to a single ID and cannot be transferred to another.