I want to add a new entry (rule type) to the dynamic audience menu. The developer documentation at https://help.totaralearning.com/display/DEV/Dynamic+cohorts suggests that should be possible -- it says:

To add a new rule type to the menu:

1. Identify the sqlhandler and ui you will need for your new rule type. (If no existing ones will work, then you'll need to implement new ones. See below.)

2. The sqlhandler and ui classes you use must have identical $params values.

3. Add an entry to $rules

4. If you've added a new group, define its name string, which will be

5. . Define the rule type's name string, which will be

That's it!

Where it says in step 3 to add an entry to $rules, I'm guessing it's not suggesting that the entry should be added by hacking cohort_rules_list() in  totara/cohorts/rules/setting.php

Can anybody help with information on how to achieve my goal without hacking core code?

Thanks.