Change network offering without changing CIDR

[Gerolamo Valcamonica]

Hi everybody,
i'm using Cloudstack 4.3 with KVM

I'd like to change network offering on a client network.
So i created a new Network offering based on 
DefaultIsolatedNetworkOfferingWithSourceNatService
Now i can go to my client network -> edit -> select 
DefaultIsolatedNetworkOfferingWithSourceNatService2 -> apply

A popup alerts me:
"Do you want to keep the current guest network CIDR unchanged?"

If i select "NO" i got this error: "All user vm of network of specified 
id should be stopped before changing CIDR!"

If i select "YES" i got this error: "Cannot specify this nework offering 
change and guestVmCidr at same time. Specify only one."

CIDR is: 10.10.1.0/24

So the question is:
can I change a network offering without changing CIDR and / or rebooting 
VMs?

As alternative question: how can change max bandwith only on a specific 
user network already using my infrastructure?

Thanks!

--
Gerolamo Valcamonica