The transaction will not be stuck, but it might not be credited properly.

What site or service are you depositing coins to? If they generate a single wallet address for you which never changes, then yes, you can send further transactions to that address without issue, and they will confirm quicker if you pay a higher fee.

If, however, the site or service generates an invoice or payment request for you, the address will only be monitored for a single deposit. Since you have already made a transaction to that address (although still unconfirmed), further transactions to that address may not be automatically detected by the system. Although the transaction will arrive normally, you may have to go through their customer support to get it credited to your account properly.