Only captain Brian O'Driscoll, Paul O'Connell and Neil Best survive from the team which lost to Scotland at the weekend as O'Sullivan checks out his options before the World Cup, which starts next month.
Marcus Horan, Rory Best and John Hayes come into the front row, with Donncha O'Callaghan, Simon Easterby and Denis Leamy completing the forwards.
O'Sullivan said: "The other players in the squad need game time and this match gives us that opportunity.
"You cannot replicate the same levels of intensity and physicality in training as you can in a match, so Thursday night will be vital for their preparation.
"This will be a full-on match and will give the team the levels of contact we need.
"The new faces in the team have really been chomping at the bit to get a game and it will be a step up for them as they come out of their pre-season, but it is something that they need."
Hooker Rory Best said: "I'm delighted to finally get on the park and play a game.
"It's been a good week, after being named in the World Cup squad and now getting the chance to move up and play my first game.
"We have moved on from all our fitness work in the pre-season and the last couple of weeks have seen us sharpen up on our ball skills and team patterns.
"I know I need to put all of that together on the park, so tomorrow night should be a tough game and allow us to get that important first match under our belts.
"The training here (Capbreton) has been great and I think we have all raised the bar another level.
"The guys who did not play last week are also eager to get a game, so we are looking forward to it."
David Wallace (ankle) and Simon Best (back spasm) took part in a rehab session as they recover from their injuries.
The match kicks off at the Stade Jean Dauger at 9pm local time.