It's exactly the same process as far as using them to drop trips/days of reserve.

The banked PB days will convert to SUPP VACA days on your timecard and they will be assigned to a vacation during the vacay bid process but if you use PB days in JAN-MAR they will use those days first (assuming you have additional banked PB days that you earned in JAN/FEB) unless you fill out the form on DELTANET to prevent them from using SUPP days and use PB days, but this is not much of an issue as you have to bid a line to use the SUPP VACA days so it's hard (impossible) to earn banked PB days in months you hold a line.

In the past, I've had the most success being able to drop high value trips with PB days in FEB, so I've been through this process in a few different years..