Welcome to the Community - First off you have never been able to manage the free version with vCenter so going to an earlier version you will still not be able to manage a free instance with vCenter.
Your options are to build your lab using the evaluation license which of course means you will have to rebuild every 60 days or contact your VMware sales rep and see if he can get you license that does not expire or lasts longer than 60 days.
I have also moved this to a more appropriate forum