should be easy to switch Game Center account. Just go to Settings -> Game Center, then choose to sign out of the current account, then sign in using a different account (the one used on your iPad). Note that you can sign on to the same Game Center account on multiple devices, so this should be fine.
What I found when I did this, is that I had to delete and reinstall the game (from App Store) to get it to load the correct base.
As already mentioned by several people, ALWAYS BACK UP YOUR BASE SECRET TO A FACEBOOK ACCOUNT by using the Facebook sync option. Important: Use one facebook account for one base ONLY. This is how you can recover your base, in case something went wrong.