Changeover

a conversion or complete change from one thing, condition, or system to another, as in equipment, personnel, methods of production, etc.:
a changeover to automated equipment.
noun
an alteration or complete reversal from one method, system, or product to another: a changeover to decimal currency
a reversal of a situation, attitude, etc
(sport)

the act of transferring to or being relieved by a team-mate in a relay race, as by handing over a baton, etc
Also called change, takeover. the point in a relay race at which the transfer is made

(sport, mainly Brit) the exchange of ends by two teams, esp at half time
verb (adverb)
to adopt (a completely different position or attitude): the driver and navigator changed over after four hours
(intransitive) (sport, mainly Brit) (of two teams) to exchange ends of a playing field, etc, as after half time

programming
The time when a new system has been tested successfully and replaces the old system.
(2003-11-12)