It depends. If you want to change multiple costumes to the same NPC costume, you can do the following with my editor:
(1) Create a filter to display only the "NPC" or "COSTUME" lines of the characters you want to change. Besides putting "NPC" as the command, you can either do this by selecting a list of references or with a specific argument.
(2) Hit the "Change All" button.
(3) Put the new NPC line in the dialog and hit okay.
(4) Clear filters, then filter to display only the "PARTSNAME" lines of the characters whose COSTUMEs you changed. Hit "Delete All."
I don't think there's fast way for changing multiple costumes to the same player costume or multiple costumes to different costumes.
I use both Zloth's and Balshor's editors. Is there any way to change multiple costumes at once? Like with Windows, you can hold ctrl then mouse over file after file to highlight them all.
Been doing them one at a time, but takes forever when you are changing 75+ costumes in a scene.
Just wondering if there is a way to do it that I am not seeing in one of the editors.