I would like to automate setting some settings, specifically add some keyboard shortcuts to ~/.config/dconf/user. Here is how it looks in dconf-editor:

Now gsettings (or dconf) can list the first one:
$ gsettings get org.cinnamon.keybindings custom-list
['custom0', 'custom1', 'custom2', 'custom3']
However, I cannot see a way to then add a new keybinding, or even to read the customX keys.
$ gsettings get org.cinnamon.keybindings.custom-keybinding:/ custom0
No such key 'custom0'
How can I add, for example, a custom4 key with binding='<Super>g', command='geany', name='Geany'?
Output to Donarssons answer:
$ gsettings get org.cinnamon.keybindings.custom-keybindings:/custom0/ binding
No such schema 'org.cinnamon.keybindings.custom-keybindings'
$ gsettings get org.cinnamon.keybindings.custom-keybinding:/custom0/ binding
''
And screenshot after the following command. Note that custom4 does not go to custom-keybindings but to the root.
gsettings set org.cinnamon.keybindings.custom-keybinding:/custom4/ binding '<Super>g'

I'm using Linux Mint as my O/S.