This was the first modification during a journey scheduled to take about eight days, according to a statement from the State Administration of Science, Technology and Industry for National Defence.
The modification was necessary because the unmanned spacecraft was affected by external factors during the transfer from a terrestrial orbit to a lunar orbit, it said.
The orbiter was launched earlier today by a Long March-3C rocket from the Xichang Satellite Launch Centre in southwest China's Sichuan Province.
The spacecraft will fly around the moon half a circle and return to Earth.
The mission is to collect data and validate re-entry technology such as guidance, navigation and control systems, and the heat shield in anticipation of a moon landing by Chang'e-5, which will collect samples and return to Earth, probably in 2017, state-run Xinhua news agency reported.
It is the first time China has conducted a test involving a half-orbit around the moon at a height of 380,000 km before having the spacecraft return to Earth.
China carried out Chang'e-1 and Chang'e-2 missions in 2007 and 2010, respectively, capping the orbital phase.
The ongoing second phase saw Chang'e-3 with the country's first moon rover, Yutu, on-board succeed in soft landing on the moon in December 2013.
Chang'e-4 is the backup probe of Chang'e-3 and will help pave the way for future probes.
