There is an option to resolve IP conflicts between clients on Cisco IOS. It needs to be configured carefully. from this source:
Configuring a DHCP Database Agent or Disabling Conflict Logging
Perform this task to configure a DHCP database agent.
A DHCP database agent is any host (for example, an FTP, TFTP, or rcp
server) or storage media on the DHCP server (for example, disk0) that
stores the DHCP bindings database. You can configure multiple DHCP
database agents, and you can configure the interval between database
updates and transfers for each agent. Automatic bindings are IP
addresses that have been automatically mapped to the MAC addresses of
hosts that are found in the DHCP database. Automatic binding
information (such as lease expiration date and time, interface index,
and VPN routing and forwarding [VRF] name) is stored on a database
agent. The bindings are saved as text records for easy maintenance.
An address conflict occurs when two hosts use the same IP address.
During address assignment, DHCP checks for conflicts using ping and
gratuitous Address Resolution Protocol (ARP). If a conflict is
detected, the address is removed from the pool. The address will not
be assigned until the administrator resolves the conflict.
We strongly recommend using database agents. However, the Cisco IOS
server can run without them. If you choose not to configure a DHCP
database agent, disable the recording of DHCP address conflicts on the
DHCP server by using the no ip dhcp conflict logging command in global
configuration mode. If there is conflict logging but no database agent
configured, bindings are lost across router reboots. Possible false
conflicts can occur causing the address to be removed from the address
pool until the network administrator intervenes.
If you have the conflict resolution configuration in place, the device will chack if the IP address is already assigned to another client or not. Also, If the clients are already assigned an IP and the DHCP for some reason stops, the client will continue to communicate normally before the renew period expires. So in case you reconfiguration affects the DHCP, you clients that already have an IP will not be affected. The new ones will get the IP from the new pool after the conflict test is passed.
However, if your setup is critical, I strongly advise you to do a test of this scenarion on a spare router before implementing it on a live system. Also try to find a low traffic period for your change.