Python - Change midi channel 1 to 10 (converting midi drum samples)

convert.py

from mido import MidiFile
from pathlib import Path

for name in Path('./ConvertThis').rglob('*.mid'):
    print(name)
    mid = MidiFile(name, clip=True)
    for message in mid.tracks[0]:
        if message.type in ('note_on','note_off'):
            message.copy(channel=9)
    mid.save(name)