The repair and replacement rules start on page 175 of StratOps, and the only mention I can find about number of teams in that section is on page 179 under "Fabrication" (which only allows one team to try at a time). There is a mention of more than one team being able to ready a unit for deployment back on page 44, and that limits the job to two teams. A team being seven personnel makes me think that for most jobs, more people would just get in the way. I think whatever you decide will be a house rule, and I'd recommend limiting multiple teams to the biggest jobs (limb/head/engine/gyro replacement o 'mechs... large aerospace units are an entirely different ball of snakes: replacing a KF drive is not something seven people could do by themselves in any case).
EDIT: Found it! The rule is back on page 168, under "Technical Personnel", last sentence of the fourth paragraph: "Two teams cannot work simultaneously on the same task, but they can divide the tasks between them to save time."