Example of how to reorder the vertex numbering in an obj file with a python script.

reorder.py

# %% reorder the vertices
import numpy as np

# %%
with open("oldorder.obj") as fid:
    lines = fid.readlines()
print(lines)

#  %%

def split_face_line(line):
    return [int(s.split('/')[0]) for s in line.split()[1:]]


def split_vert_line(line):
    return [[float(s) for s in ss.split()] for ss in line.split()[1:]]


# %%

tri, pts = [], []

for line in lines:
    line = line.strip()
    if '#' in line:
        continue
    if 'vt' in line:
        continue
    if 'f' in line:
        tri.append(split_face_line(line))
    if 'v ' in line:
        pts.append(split_vert_line(line))

tri = np.array(tri, dtype=np.int32) - 1
pts = np.array(pts, dtype=np.float32)


# %%

# the current zero indexed order...
reorder = np.array([
    55, 45, 44, 43, 42, 41, 40, 39, 0, 7, 8, 9, 10, 11, 12, 13, 23, 60, 59,
    58, 57, 56, 25, 26, 27, 28, 29, 24, 6, 5, 4, 48, 49, 3, 17, 16, 46, 64, 65,
    47, 67, 66, 15, 36, 35, 14, 37, 38, 52, 51, 50, 2, 18, 19, 20, 21, 22, 1,
    54, 53, 62, 61, 30, 31, 32, 33, 34, 63])


inv_reorder = np.zeros(68, dtype=np.int32)
for i, k in enumerate(reorder):
    inv_reorder[k] = i


new_tris = inv_reorder[tri]
new_pts = pts[reorder]


#%%

with open("neworder.obj", 'w') as fid:
    for p in new_pts.squeeze():
        fid.write(f"v {p[0]:0.3f} {p[1]:0.3f} {p[2]:0.3f}\n")
    for t in 1 + new_tris.squeeze():
        fid.write(f"f {t[0]:d} {t[1]:d} {t[2]:d}\n")