How sasuke is still able to use curse mark?
It was not Sasuke's curse mark that was used, he's with Jugo when Susanoo was infused with sage chakra, so Jugo's chakra was used to gain Senjutsu Susanoo and form the same pattern as Sasuke's curse seal.

Jugo in Sasuke's Susano


Orochimaru explaining Jugo's chakra



Source: Ch. 648