A team spokeswoman said Jain, an Oxford physics graduate who joined the team in 2016, would be in charge of strategy at the track.
Rueda remains part of the team with a factory-based sporting role at Maranello.
Strategy is one of the areas new team principal Fred Vasseur has been looking at since taking over in January to address some glaring and costly errors last season.
Ferrari started that season strongly, winning two of the first three races, but ended up distant runners-up to champions Red Bull.
They were let down also by reliability and driver mistakes but strategic blunders included a pit call in Monaco that cost Charles Leclerc (25) a home victory after starting on pole position and a tyre gamble that backfired for qualifying in Brazil.
Vasseur, who has joined as a replacement for Mattia Binotto, said this month that Ferrari would be making some marginal changes to the race team.
"Very often, when you are speaking about strategy, it's much more a matter of organisation than just the guy who is on the pit wall," he said.
"I'm trying to understand exactly what's happened on every single mistake and what's happened last year. And to try to know if it's a matter of decision, if it's a matter of organisation, or of communication."
Ferrari have not won a championship since the 2008 constructors' title and the pressure is on Vasseur to fix the errors and end the long drought for the sport's oldest and most successful team.
The team started pre-season testing in Bahrain on Thursday with Carlos Sainz (28) behind the wheel for the first session at the Sakhir circuit.
