Brown was initially told the January 18 clash against St Johnstone would be his final match and that his contract would not be renewed.
The surprise decision was followed by news that managing director David Southern and director of football John Murray had agreed to take a pay cut.
However, administrator Bryan Jackson performed a partial U-turn the day after the Perth encounter - following talks with a delegation of Hearts players - by announcing that Brown would stay on until his contract expired at the end of this month.
And Brown will now be in the dugout for Sunday's League Cup semi-final against Inverness after he was kept on further.
A statement from BDO read: "The administrators of Heart of Midlothian FC have extended the contract of assistant manager Billy Brown to the end of February.
"This will allow him to assist Gary Locke with the February 2 League Cup fixture."
Jackson added: "It makes sense to offer Billy an extension of a month on his contract to cover this crucial fixture."
The 63-year-old initially worked on a voluntary basis when he rejoined Hearts for a third coaching spell in the summer before being handed a short-term contract in September.
The new one-month deal will allow the prospective owners, Foundation of Hearts, to decide on Brown's future if and when their protracted takeover is completed.