  We show that isotope-exchange reactions between ground-state alkali-metal,
alkaline-earth-metal, and lanthanide heteronuclear dimers consisting of two
isotopes of the same atom are exothermic with an energy change in the range of
1-8000$\,$MHz thus resulting in cold or ultracold products. For these chemical
reactions there are only one rovibrational and at most several hyperfine
possible product states. The number and energetics of open and closed reactive
channels can be controlled by the laser and magnetic fields. We suggest a
laser-induced isotope- and state-selective Stark shift control to tune the
exothermic isotope-exchange reactions to become endothermic thus providing the
ground for testing models of the chemical reactivity. The present proposal
opens the way for studying the state-to-state dynamics of ultracold chemical
reactions beyond the universal limit with a meaningful control over the quantum
states of both reactants and products.
