In theory, it is not possible to remove mass from an atom without fundamentally altering its composition or violating the laws of physics. According to the law of conservation of mass, mass cannot be created or destroyed, but only transformed or rearranged. In the case of an atom, its mass is primarily attributed to the protons and neutrons in the nucleus, along with a smaller contribution from the orbiting electrons.
To remove mass from an atom, you would need to remove protons, neutrons, or electrons. However, altering the number of protons would change the atom's identity, turning it into a different element entirely. Similarly, removing neutrons may result in an unstable isotope of the same element. Removing electrons can result in the formation of charged particles, but the mass would remain the same.
While nuclear reactions, such as radioactive decay or nuclear fission/fusion, can change the composition of an atom and release energy, they do not remove mass from the atom itself. The total mass of the system involved in these reactions remains conserved.
In summary, removing mass from an atom without changing its identity is not possible within our current understanding of physics.