Is this a viable configuration - ER Poe5

I currently have my ER PoE-5 setup like this:

eth0 - ISP

eth1 - nothing

eth2-4 setup as switch for my local lan with:

--eth2 - connected to 8 port switch #1

--eth3 - PoE enabled to AP

--eth4 - connected to 8 port switch #2

I just got a cloud key to replace my vm with controller as it's become troublesome for me to keep the vm going reliably on my machine(hardware issue) and I scored it for a good deal. I'd like to use eth1, enable PoE and keep my configuration the same. Can I setup a secondary private subnet on eth1 and route to it from my local network without causing any other ill effects?

So for instance

current local lan is 192.168.20.0/24

add subnet 192.168.30.0/24 to eth1 and plug cloud key in there.