Could mars be made habitable if we moved more mass to its surface from the asteroid belt?

If humans could devise a method for influencing asteroids to relocate, and aim them at Mars, we could "add" mass to the planet, and/or make a large moon for a binary planet system. My idea is to influence the gravity well of the inner core of Mars to create heat, and cause a magnetosphere to form. With more of the suns rays being deflected, and more mass to hold a larger atmosphere, I believe Mars will terraform itself as the dust settles, and become habitable. In my opinion since Mars does not have the same density of metal at its core as earth, the amount of mass needed to create a weak Magnetosphere would be on the order of double to triple it's current size. The technology needed to move material from the asteroid belt, would not be achievable in the terms of propulsion. An asteroid the size of Texas would need a ship of comparable size with a specific gravity influence large enough to attract it and travel at a reasonable speed. The effect of relocating mass to Mars, would also affect Earths orbit outward, and Mars' orbit inward towards the Sun. This is not a bad thing, as you might assume. As the Sun ages, it is getting brighter, and Earth hotter. Earth will need to expand it's orbit in the future to maintain it's current climate. Do you feel my idea holds weight, and can it be done?