Well rather than changing the DHCP scope range you could just add a second card into your server and have that as your gateway, alternatively get your ISP to change the IP on their router so that it's using the 192.168.0.1 address (you're the customer you have every right to make that request).
If however you want to go with the new addressing scheme you should start reducing the lease time on the current DHCP scope to hours rather than days, ideally you should give it a 6 hour lease time, once you have reduced the lease time and ALL of the machines are getting their address based on the new lease time you can start to make the changes. The reason you want 6 hours is because this will allow you to make the changes one evening and have the new scope rolled out across the environment when you come back into the office the next day.
Now you 'should' be using reserved addresses for your servers as well as your workstations, if you are then what you're going to have to do is create your new scope using the new range and add the servers onto the reserved list (you will need the MAC address of all those machines).
If you have any routers\switches in your environment you're also going to have to change them to allow for the new range.
If you can't wait for the reduction in lease time then you can go down the route of the new scope now, what you would need to do however is stop the current scope and visit every single machine and do an ipconfig /release and /renew on it (some of the time a /renew won't do it first time which is why the /release is used first).
Simon
The real world is not about exam scores, it's about ability.