Can I still apply for a refund if the registration sticker was attached to the plate?
No, in that case, the sticker can't be removed and you won't be able to apply for a full refund.
What is needed to apply for the 2-year refund?
The 2-year registration fee refund can only be applied if the registration was never used and it hasn't been more than 60 days from the date the registration was issued.