First of all, i already know how to make universal apps, my question is if having an iPad app in the store i'm allowed to add iPhone support in an update ( make it universal).
Also, if my iPad app doesn't has in-app purchases, i'm allowed to add new ones in an update ? ( i'm pretty sure the answer is yes but wanted to ask just in case)
Thanks for your orientation !
Yes, you can do both of those things. You'll have to sign additional contracts with Apple to offer in-app purchase, but that's done through iTunes Connect and doesn't affect the binary you submit.