If it's freelance then you're effectively a company negotiating task<->money with another company. If they change the scope (add new requirement) you can absolu

If it's freelance then you're effectively a company negotiating task<->money with another company. If they change the scope (add new requirement) you can absolutely push back and either tell them the work will take longer or ask for higher fee. It's easier if you get paid per hour/day and you add more hours/days to the bill than raising the per-hour/day fee.