Hello guys! A client mistakenly uploaded a bank statement with lines with a year 2020 instead of 2021 and saved so journals generated all have the 2020 date. If we change the dates from 2020 to 2021 via csv import, would that not create any issues? Thank youu!

Make sure you change the date, and the posting period fields if they exist on JE, If the accounting period is still open I don't see any problems with this. Can you test in sandbox?