If I change a router's subnet mask to one that includes the old one, will the hosts with the old configuration still work?

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http://serverfault.com – Currently I have a router that is addressed as on a network. All of my hosts have default gateway with mask I want to know: if I change my router to will the hosts that have subnet mask corresponding to /24 still work in the interim (before I reconfigure)? (HowTos)