The former Supercars full-timer is set to team up with Super2 regular Aaron Love in BRT's wildcard entry for the Sandown 500 and Bathurst 1000.
The deal marks a change of plans for BRT, which had originally applied for its wildcard on the basis that Tim Blanchard would partner Love.
Blanchard will instead co-drive BRT's primary entry with Todd Hazelwood at the enduros.
Kostecki has been missing from the Supercars grid this year after a shock split with Tickford Racing, just a year into a multi-year deal, at the end of 2022.
“I am super excited to be back racing in the Supercars Championship for the enduro season with the Blanchard Racing Team, co-driving with my good friend Aaron Love," said Kostecki.
"I am very thankful to the Blanchard family and BRT for the opportunity.
“Gen3 has brought new excitement to the sport, so I am looking forward to getting back behind the wheel of a Mustang and getting some good results.
“I’ve been close friends with Aaron for fair few years. He has done a fantastic job in Carrera Cup dominating the front of the field, and now in his first year in Super2, he’s finding his form very nicely, so I am looking forward to racing alongside him and helping out as much as I can.
“I’ll be going to the workshop soon to meet the whole team, do a seat fit with Aaron and get prepared as much as we can. With being the first year of Gen3 enduros, I am not sure what to expect, but the team has done a great job building the car and getting organised for the programme."
The wildcard programme marks another step in the growth of BRT, which is expected to step up to two main game entries next year as part of a reshuffling of Teams Racing Charters.
"We are excited to give Aaron his first opportunity in the main series and welcome Jake to BRT," said team owner Blanchard.
"Both are young guys wanting to make an impression and we are keen to support young drivers by giving them the opportunity.
“Expectations are realistic but Aaron has done a great job so far this year and Jake is experienced enough to know what to do, so they could surprise a few people.
“The wildcard programme is another key step in the expansion of BRT. The resources in preparing a second car is not small but that’s why we are keen to utilise this programme to develop the team.
“For myself, I am looking forward to joining Todd and experiencing the Gen3 car. We have driven together before and obviously worked together this year so it should be a fairly simple process which will hopefully work to our advantage.”
