Changing Network Mask

Hi,

I know just enough about networking to be dangerous, and this is a more general question I know, but since I have a UTM9 (SG230) I'll start here.

For decade-old and boring reasons, we have a LAN 192.168.0.0/19 for only a few hundred hosts (70 office staff with laptops and phones, some tablets, a few servers, printers, etc).

For years I have been trying to change this, and I think I'm about ready. I would like to change it to 192.168.16.0/22. Still room to grow but not so ridiculous as 8,190 addresses. Plus I can get my network away from common home network ranges to avoid VPN/NAT issues.

I am finally at the point where all my static and dynamic addresses fall between 192.168.16.2-192.168.19.254.

I already have 192.168.16.1 added as an Additional Address on the LAN interface. That'll be the new gateway address on the LAN.

DHCP clients are currently given 192.168.16.1 as the DNS Server and 192.168.0.1 as the gateway address.

My plan is to...

Swap the LAN's interface address and Additional Address (so 192.168.16.1 becomes the "real" one and 192.168.0.1 becomes the additional).

Change DHCP settings to point users to the new gateway address (192.168.16.1).

Since all static IPs are already in the range 192.168.16.2-192.168.19.254, they should still see and treat everything ok even before I change their masks, right? I have a couple windows servers in the network, including an AD DC, but I assume I can take my time in changing their masks since the /22 network I'm making is within the /19 network I currently have. Right?

Or am I in over my head?

Thanks,

Jeff