UPC vs ASIN on product label

Hi, at our company, we made a huge mess of our listings because we failed to register our UPCs which were taken by other companies. And so we removed the now wrong UPC from our product labeling and put the ASIN on instead.

Is it possible to add back a correct UPC and also keep the ASIN on labels? We are worried that we will mess up our inventory there.

Does anyone else just apply the ASIN and use no UPC?

Looking for what the best practice is so as to reduce the unending headaches we’ve been having.