Вы можете просто сформировать все переупорядочения с помощью возможностей индексирования numpy.
import numpy as np
from itertools import permutations
# first generate all sets of rearrangements you'd like to make..
orderings = [p for p in permutations(np.arange(3)) if p!=(0,1,2)]
# [(0, 2, 1), (1, 0, 2), (1, 2, 0), (2, 0, 1), (2, 1, 0)]
# rbg, brg, and so on.
# then reorder along axis=-1 using these. (0,1,2) --> (0,2,1) and so on.
for order in orderings:
reordered = im[...,order]
# then save each an appropriate filename
cv2.imsave('filename.jpg', reordered)
del reordered, order