|192.168.0.0/23 gives you the following network:|
192.168.0.1 to 192.168.1.254
Do you see any conflict with your existing network?
What ijack is suggesting is to simply add another network (ie: 192.168.5.0/24)
Changing your existing "corporate" network the way you're suggesting might work if the corporate is completely segmented from all other branch networks. If however, they're not separate, then you can't do it and your best bet would be to add another network.
I have to ask, and I do not mean to be rude but, your questions make me think you have little to no experience with networking. If that is the case, you might want to hire a competent consultant to come in and get you setup so you know it's done correctly.
It matters not how straight the gate,
How charged with punishments the scroll,
I am the master of my fate;
I am the captain of my soul.