I have one idea for a planet which may turn out to be a massively reengineered and terraformed Mars, which would have double its mass to be more Earth-like, an installed magnetosphere, etc. It would have a massive endoskeleton which expands the surface (with trenches everywhere of course) to an Earth-like volume as well. (Let's assume the megascale engineers delivered the extra mass from the asteroid belt.)
How would Mars' orbit be affected by such a project? I like to imagine the engineers and settlers of this reformed Mars would've also been able to synchronize the planet's days with that of Earth's, but would Mars fall closer towards the sun from the extra mass?
Also, would it even be necessary to engineer Mars on such a massive scale? Practically aside, is it important for Mars to have the same mass and size of Earth for long-term human colonization, or could humans live pretty much the same long-term (without health problems or morphological changes after hundreds of generations)?