- Create a blank upgrade with a name like "ability_unlock"
- Have a base ability on the squad that adds this upgrade when clicked and (is set in the requirements to be hidden when then the upgrade is present)
- Set the sub abilites to require the upgrade to be present to be seen.
- Create an exit ability (that can only be seen when the upgrade is present) which removes the upgrade to return to the original ability selection of the squad.
Its not as pretty as new ui, but it does at least allow you to have more abilites on a squad.