I don’t know how much this will help much I was looking for a solution myself when stumbling upon this thread. I popped back into Unreal 4 and ended up finding something.
If you select all the sprites in a particular set (example: a walking animation) in the Content Browser, you can then Right Click the selected sprites. Go to “Asset Actions > Bulk Edit via Property Matrix…”. A new window will pop up. From here you can go to the panel on the right and hit the Sprite drop down. Change the Pivot Mode to whatever you need and save.
If you’re using the Custom Pivot like I see in the screenshot, this should allow you to find one coordinate and then bulk change all of the Pivots to be the same without doing it individually. Like I did. Before I found this tool right after I was done doing it individually. Oye.