Before splitting a core, a sacred artist must have access to a technique that prepares the body to handle the stress of splitting. An example of a way to do this is the cycling technique Heart of Twin Stars which prepares the body for a core split, though other such techniques exist.
When a core is split, it is not completely efficient. When one core is made into two there is a loss in overall madra capacity equivalent to about 2% of the original core.(E.g Original Core = 100% when core spilt becomes 49% + 49%) The two cores that result can be grown back to full size through cultivation aids and cycling. And need to do so before being split again.