Yes, after joining AllTrack as a creator, you can return to AllTrack anytime to setup a publisher.
As a reminder however, if you are an AllTrack creator, there is no requirement to setup an AllTrack publisher to be able to collect your publisher's share of your royalties. With AllTrack, you can collect 100% of your combined creator and publisher shares of performance royalties just by registering for a free AllTrack creator account.
You can register for a free AllTrack creator account here.
You can learn more about the benefits of setting up a publisher account with AllTrack here.