Eh... no
If you want to fly online, you should be as compatible to each other as possible.
That means: If you want to fly online with other Stock Game Users, use the same stock version like they do.
And if you want to use Cassie's features, it's highly recommended that all users use Cassie.
In General terms, IL-2 always used to be incompatible between different game versions or modpacks.
Ultrapack 3.x is the big exception to this rule: We retain as much backward compatibility as possible.
We achieved this by keeping the network protocol fully compatible with Stock 4.10.1.
"Fully Compatible" means: If a Stock 4.10.1 Player plays with a Cassie player, everything's fine as long as they stick to Stock Content.
In general, all content (objects, maps, airplanes, whatever) need to be limited to the smallest, most common intersection of content being available to all players.
Example:
Stock 4.10.1, Ultrapack 3 RC4 and Cassie Player together: Content needs to be Stock 4.10.1 only.
Ultrapack 3 RC4 and Cassie Player: Content needs to be Ultrapack 3 RC4 only.
Cassie unpatched and Cassie Patch 2 Player: Content needs to be Cassie unpatched only.
Cassie Patch 2 w/o Hotfix and Hotfix 19 Player: Content needs to be Cassie Patch 2 only.
You get the gist.
That being said, whichever game version you're coming from, once you install the Cassie Superpack, you get a full blown Cassie which fulfills the above mentioned criteria.
No need to patch your game up or down in advance.
Mike