Changing External VLAN to a Trunk (Cisco trunk) - No downtime

We have an HA pair running 10.2.1. Our External VLAN is nearly out of IPs. As a result, we need to add an additional VLAN. The problem is the external trunk (F5 trunk) is currently untagged. I'd like to change it to a tagged interface and avoid downtime. Here is a snippet of the current External settings (identical on our standby unit):

 

 

vlan External {

 

tag 4094

 

mac masq xx:xx:xx:xx:xx:xx

 

failsafe enable

 

failsafe failover

 

trunks external_trk

 

}

 

 

 

 

 

Does the plan below make sense? I don't expect any downtime other than the two failovers. What I'm concerned about is unexpected failovers. I ran into some trouble a while back when I made the bad assumption that I could change the management interface without affecting anything!

 

 

 

1. On unit 2 (standby), make the following changes to the External VLAN:

 

tag 200

 

trunks tagged external_trk

 

 

 

2. On the port channel on the switch connected to unit 2, change it from access mode to trunk mode.

 

 

 

3. Test connectivity to unit 2's self IP on the External VLAN.

 

 

 

4. Failover to unit 2.

 

 

 

5. Perform steps 1-3 on unit 1 (currently in standby).

 

 

 

6. Fail back to unit 1.

 

 

 

7. At this point, I can add an additional tagged VLAN on external_trk and setup the self/floating IPs. This is a normal action that can be done anytime for us.