It depends a bit on your configuration if the desired configuration is possible.
This feature was created having in mind that we have the ability to mix and match WAN connections used in the PepVPN profile.
If you have multiple WAN connections (WAN 1, 2 and 3, with WAN 1 being the most reliable, fastest connection and WAN 2 and 3 slower lines used for redundancy) you can create seperate PepVPN profiles that use different WAN connections.
PepVPN profile 1: uses WAN1 with the highest priority and WAN 2 as backup
PepVPN profile 2: uses WAN 2 with the highest priority and WAN 1 as backup
PepVPN profile 3: uses all WAN connections that are available
If you have a situation as above you could create an outbound rule for traffic matching TCP port 3389 and UDP port 3389 to use PepVPN profile 1, and other traffic could use another profile.
Traffic that you want to prioritise will then use your faster, more reliable WAN connections and you could use slower WAN connections for other traffic with less priority (backups or print jobs for example).
This is only beneficial in situations where you use multiple WAN connections, the more WAN connections you have available, the more options it gives you.
It doesn’t work in the traditional sense of QoS where you can send different traffic simultaneously through the VPN tunnel and add a different priority to each type of traffic.