virtual switch with preprovisioned conf: promote line cards to routing engine and demote routing engine to line cards roles

Hello community,

I have a VC with x2 4200 (member 0 & 1) and x2 4550 (member 2 & 3).In preparation for upgrading the x2 4200 to 4550, I want to promote member 2 and 3 to routing-engine and demote member 0 and 1 to linecards.

This is the current preprovisioned vc config:

set virtual-chassis preprovisioned
set virtual-chassis member 0 role routing-engine
set virtual-chassis member 0 serial-number WWWWWWWWWWWW
set virtual-chassis member 1 role routing-engine
set virtual-chassis member 1 serial-number XXXXXXXXXXXX
set virtual-chassis member 2 role line-card
set virtual-chassis member 2 serial-number YYYYYYYYYYYY
set virtual-chassis member 3 role line-card
set virtual-chassis member 3 serial-number ZZZZZZZZZZZZ

What is the less disruptive way of doing it?. I was thinking on changing the preprovisioned , so the x2 4550 are role routing-engine and x2 4200 are line-card. But then after that, not 100% it will work straightaway. Does anybody had faced the same change?

set virtual-chassis preprovisioned:

set virtual-chassis member 0 role line-card
set virtual-chassis member 0 serial-number WWWWWWWWWWWW
set virtual-chassis member 1 role line-card
set virtual-chassis member 1 serial-number XXXXXXXXXXXX
set virtual-chassis member 2 role routing-engine
set virtual-chassis member 2 serial-number YYYYYYYYYYYY
set virtual-chassis member 3 role routing-engine
set virtual-chassis member 3 serial-number ZZZZZZZZZZZZ

Now giving it a second though, maybe I can do something like this

step 1)
member 0 role routing-engine (currently master)
member 1 role routing-engine (currently backup)
member 2 role line-card
member 3 role line-card

step 2)
member 0 role routing-engine (currently master)
member 1 role line-card
member 2 role routing-engine (will become backup)
member 3 role line-card

step 3)
member 0 role line-card
member 1 role line-card
member 2 role routing-engine (will become mastter)
member 3 role routing-engine (will become backup)

Do you thinki this will work? Maybe i'll need to console to the members and restart member/s? Again, this is a core chassis so i'm looking for minimum downtime.

Many thanks in advance,

Jaime