it should not damage the board, and we are adding the 3rd channel in backup. Some people already used a prizm with 3 strips with no issue, a 3rd driver makes just more sense for 3 strips and improves the power management.
The latest firmware from earlier this month should normally have this (EU production and possibly USA production as well), you can test which board you have by using channel 3 on a single strip to see if it gets powered.
fdrive to 111 ? not sure I understand that one