The move comes after the resignation of Union of Moderate Party MP, Robin Kapapa.
Our correspondent reported Loughman made the appointment to shore up his numbers amid reports more government MPs could move to the opposition of Ralph Regenvanu.
He says Hymak is believed to be one of those whose loyalty was wavering.
Recently the UMP executive in Kapapa's Tanna constituency called on other party MPs to join the opposition.
With the defection of Kapapa and Christopher Emelee from the government, the Opposition has 24 MPs compared with the government's 28.
Meanwhile there are mounting public concerns over the visit of 130 politicians and civil servants to the island of Ambae this week.
Prime Minister Bob Loughman left Port Vila this morning to lead the biggest government delegation to visit the island since independence 40 years ago.
Social media had been rife with concerns raised over the spending of public funds during a financial crisis triggered by Covid-19 and damage caused by April's Cyclone Harold.
Over $US5700 a day was being paid for travelling allowances although people have to pay for their accommodation and transport.
Some of the delegation have been on the island since last week.
Loughman was expected to open new cooperatives on East Ambae and West Ambae as well as a new office of tourism.