Ive done something similar, using the osmc skin you can just add an entry to the sub menu of one of the main menu items…eg, Settings.
From there you can select ‘Change action’, then ‘Custom item’, then enter:
XBMC.RunScript(/home/osmc/path/to/script.py)
One caveat is I think its a Kodi limitation that only python scripts can be run like this, but you can simply call your bash script from the python script via:
import os
os.system('path/to/bash.sh')
or something similar…adding a Kodi notification via the script is pretty straightforward as well.