Apps are tied to the account they were purchased through, if you change primary accounts, you will lose your paid apps. Not sure if Google will help you out with migrating them or not, but I suspect you're SOL.
You will keep the apps that you have downloaded, but you will not be able to reinstall them without paying for them again on the new account.
Remember, this is only for the primary account. I have 3 Google accounts on my phone, and since I always use the same one as the primary, then I always have access to my paid apps.