Magistrate Miranda Moody said Costellia knew he was violating the terms of his extended supervision order when he used his wife's Facebook account to send messages despite being banned from social media.
"Any use is prohibited and he would have known that given the surreptitious way he accessed Facebook," Ms Moody said in Sydney's Downing Centre Court on Tuesday.
However, the messages were of a "mundane quality".
"There are breaches and there are breaches," Ms Moody said.
He pleaded guilty and was released with time served after spending a year and six days on remand.
Costellia's supervision order was suspended while he was in custody but will resume upon his release.
He was originally placed under the order as a condition of being allowed to return to the South Coast property that serves as a commune for his cult followers.
The self-professed prophet - formerly known at William Kamm - calls himself "Little Pebble".
Costellia, who claims to communicate with Jesus Christ and the Virgin Mary through visions, was released on parole in 2014 after being convicted of sexual and indecent assaults committed against two children in his cult in the 1990s.
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