Hi there @jasonx3!
Don here from Shopify.
It would not be possible to transfer an existing store to a development store on a partner account in any circumstances.
You can still create a new development store on your partner account, and you can transfer any info possible from your original trial store.
Are you looking to create stores for clients, apps for our store, or any other particular aspect of our partner program?
Don from Shopify once more.
If you check out the guide to backups and duplication I shared above, you will see what is possible to backup and duplicate and what is not.
Spend some time checking out the links and guides shared here, as they will likely answer a lot of the questions you may have.
Let me know if anything else can be clarified for you here!