Trimble replaces the injured Timoci Nagusa on the right wing, while Ferris returns from injury at number 6, with David Pollock moving to openside flanker and number 8 Chris Henry captaining his province once again.
The two other personnel changes made by Brian McLaughlin see Nigel Brady starting ahead of Andy Kyriacou at hooker and Ed O'Donoghue gets the nod over Ryan Caldwell in the second row.
A knee injury has sidelined South African prop BJ Botha for this crucial clash, so Declan Fitzpatrick continues in the tighthead role.
Commenting on Saturday's game, Ulster coach McLaughlin said: "We know how good Stade Francais are, we know they are a great side with great ambitions for the season. But we have the same ambitions.
"We have them here in Belfast on Saturday, and we have just got to get out onto the pitch and play. We have to out-play them by being accurate and smart, and taking the home advantage. We have to be fearless."
Tickets are still available for the game from the Ulster Rugby Ticket Office (Friday (9am-5pm), Saturday (9am-11am)), by telephoning the Ticket Line (tel: 028 90493 222, Option 2) or by clicking here.
Tickets will also be available to purchase on the gates on matchday from 12pm.
ULSTER (v Stade Francais): Clinton Schifcofske; Andrew Trimble, Darren Cave, Ian Whitten, Simon Danielli; Ian Humphreys, Isaac Boss; Tom Court, Nigel Brady, Declan Fitzpatrick, Ed O'Donoghue, Dan Tuohy, Stephen Ferris, David Pollock, Chris Henry (capt).
Replacements: Andy Kyriacou, Bryan Young, Justin Fitzpatrick, Ryan Caldwell, Willie Faloon, Paul Marshall, Niall O'Connor, Jamie Smith.