l subject matter of dropping and adding parties." Id at 873 (citation omitted). See also Galustian I. Peter, 591 F.3d 724, 730 (4'h Cir. 2010), and Frank I. U.S. West. Inc., 3 F.3d 1357, 1365-66 (10th Cir. 1993) ("To the extent that Plaintiffs' motion to supplement sought the addition of a party, it is controlled by Ru