Is it legal to lift the spring off the trapping (snap) portion of the mousetrap and attach the extension bar directly to the spring?

No, lifting the spring off the snap portion of the mousetrap would be a violation of 3.c.line 2 by modifying the mousetrap so that it would not function as intended and attaching the extension bar directly to the spring would be a violation of 3.c.lines 4-6, which states that items, other than the extension bar attached to the snap portion, may not be added to the mousetrap.

May students connect the two snap bars and have one extension bar or connect the two extensions?

Yes, students are allowed to connect the 2 snap portions of the mousetraps with either one or two extension bars. The mousetraps may not be connected in any other way.