Rorary, you should never need to edit the code. All of the settings are accessed in the chat via the help screen:
!group-init --help
Once the code has run once, it sets all the defaults into the state, which is persisted and changed by the settings code. Changing the code won't change what is already stored in the state.
There is a button for changing the die size that says
Set Die Size. Click that and it will prompt you for the new size, put 6 in.
For the attribute to add, it's a bit clunky as I have yet to replaced the system I wrote for it over a year ago. First you need to remove the default rule that is there:
!group-init --del-group 1
Then you need to add a new attribute:
!group-init --add-group --Bare initiative
That should get you setup the way you want it.