The help desk uses your email address to identify you. If you change your email address and just start sending in requests from the new address, you will end up with two separate accounts and you will not be able to see all of your ticket history in one place.
To prevent this, you should change your email address in your account profile then log out of the help desk and log in again, before you send any requests from the new address. This will update your email address in the help desk.
If you do end up with two accounts, they can be merged on request (choose the General category), but you will need to supply evidence that you own both accounts. For example, you could quote some text from a help request that was submitted from your old address when you submit a request from your new address asking for the merge to be done. Alternatively, if you can still receive email at the old address we can send an email to that address asking you to confirm the merge request and the new email address that you made the request from.