Yyou can move iCloud data between the 2 accounts but ca't moved purchased content such as movies, music and apps, so if you have purchased content from one ID only, you may be OK.
When you delete the account from your device, you will be given the opportunity to save Safari data, reminders, calendars and contacts to your device, which you can later merge with the other account once you login.
You won't be able to save your photo stream photos in the same way, so if you have any photo stream photos that are not already in your camera roll, you should move them there before you delete your account.
Your iWork documents can be saved to iTunes on your device, but if you have them on a Mac they would be much easier to save to your desktop there. You can move them back after you switch.
Notes can be shared to messages or mail and copy and pasted back after the switch. Although if you have a Mac, you may find it easier to do there. You could also use a temporary secondary account (see last item) to log into both accounts and copy and paste directly into your other account.
You can set up Mail forwarding at iCloud.com mail preferences (little gear icon-bottom left) to receive mail from your old address to your new one.
As an alternative to just switching, you might consider switching and adding your previous account back as a secondary account at settings > mail, contacts, calendars. You would still need to move your photos and iWork documents and save your safari data, but you'd have access to your old mail, contacts, calendars, reminders and notes.
