Hi,
the new rule will only affect people who apply for benefits after January 1, 2019. If you are in a current period with Unemployment benefits ("dagpenge"), then you will have the right to receive benefits for the current 2-year period.
Only if you will earn rights to a new period with benefits ("dagpenge"), then next time you apply for a new period with benefits, you will be affected by the new rule.
Read our article concerning the new residence requirement
And therefore off course also you can't be required to pay anything back of the unemployment benefits you already have received.
Best regards,
Anders, www.a-kasser.dk