It applies to Sephardim.
It may also apply to Ashkenazim. That depends on your view of the Rabbainu Gershom’s cherem. Was it for 250 years (ad sof elef haChamishi), 1000 years (which recently ended), or until Moshiah?
But look at the next Siif (76:7). I, as a Sephardi, can’t marry another w/o my wife’s permission because I live in a place where the custom is to marry only one. It seems implicit in my marriage agreement with my wife.