Mackintosh came off the bench in last week's game against the Cheetahs in his comeback from injury and showed enough in his 30-plus minutes on the field to warrant a starting spot.
His return means an unlucky demotion to the bench for prop Chris King, who has had a stand-out year, impressing around the field and putting pressure on opposition scrums.
He is bound to get some playing time during the match.
Triggs comes in for Josh Bekhuis, who also moves to the bench.
The Southland lock, like King, is unlucky to move to the sidelines after an impressive series of matches, but Triggs' ball-running and physical style will be an asset against the tough South Africans.
The backs remain the same as last week, with coach Glenn Moore sticking with the inside back combination of Mathew Berquist and Daniel Bowden.
Berquist and Bowden create two kicking options in the inside backs and Moore said last week he was happy with the variations the duo brought to the game.
Bowden has recovered from a kick in the back, which sent him from the field last weekend, while centre and vice-captain Jason Shoemark has also recovered from an injury, getting over an ankle niggle.
There are five Hawkes Bay players in the starting XV, so there should be plenty of supporters travelling through the Manawatu Gorge.
Manawatu's only player in the Highlanders squad, Johnny Leota, will start on the bench.
Winger Fetu'u Vainikolo will be on the bench, replacing Lucky Mulipola.
Vainikolo will have got a wake-up call last week after being dropped because of poor form and will want to get on the park at some stage.
The Highlanders are facing the competition leaders, and with the bye next week this is a make-or-break game for the southern franchise.
The Highlanders are in eighth position on the table and with no clearcut top four emerging, a win tomorrow night will put the southerners in the running before their week off.
The Bulls have made three changes to the side which beat the Hurricanes last weekend.
The Pretoria-based side is still without injured captain Victor Matfield and star winger Bryan Habana but has an imposing-looking pack, and strong backs.
Matfield has a shoulder injury, while Habana broke the ring finger on his right hand at the start of this month and is recovering slowly.
In the changes of the Bulls, Jaco Pretorious comes into centre for JP Nel, while Rayno Gerber moves into tighthead prop, replacing Werner Kruger.
Dewald Potegieter comes on to the blindside flank to replace the suspended Deon Stegmann, who was sent off in last week's match after a high tackle on Hurricanes centre Conrad Smith.
Stegmann has returned to South Africa after being suspended for three weeks and he has been replaced in the touring squad by Jacques Burger, who moves straight on to the bench.
The Bulls are unbeaten after five games and play a typical South African game - big and strong up front, a resolute defence, and a strong kicking game.
