That's why you're requred to get RAD approval first!  

You are attempting to substitute your work shift for a training day.  You're schedule is at your base, and is a 12-hr shift.  It is not a training day.  Matter of fact, training is expressly excluded from your obligation to provide 182.5 shifts per year.

Appendix A

Work Shift: The Pilot’s salary is based upon 182 ½ work shifts per year. A “work shift” is defined
as a minimum of twelve (12) and up to a fourteen (14) hours of duration. A “work shift” does not
include training, meetings and travel to or from training or meetings on an off work day.

So, you are trying to skip on the scheduled work shift by substituting a training or travel day in as one of your work shifts at the base, and that would need RAD approval.  Maybe they have coverage, maybe they don't, so it's up to the RAD to decide whether to keep you on your assigned work schedule, or allow you to skip out on it for training.