I’m not sure you’re asking the right question. Do you mean to ask if you can add tables or columns later? (i.e. Change the structure of an existing database)
The answer is yes in all cases – you’ll just have partially empty records from earlier so be aware that queries/code might not work as expected between old and new database records.
And if you really mean to ask if you can add more data later, without changing the database table structure, that is a yes too. That’s the nature of database driven websites/apps – you can add more data records any time you want.