Are you asking about a user who puts in their own IP, instead of using DHCP. If so, then it will be a fixed IP, and DHCP won't be involved. DHCP will only hand out IPs to clients, who request one.
Or are you asking about a user who takes his machine off one network, using DHCP, and connects it to yours, where, initially, the client will try and renew the existing IP. In this case, DHCP should reject that request, and the client will then request a new IP, which will be the one specified in your DHCP configuration.