Hypothetically speaking, if we would find another planet, the size of Earth, with atmosphere as dense as Earth's atmosphere is, and we would insert (in some hypothetical way) nitrogen, oxygen and CO2 in the quantity they are found on Earth, and (again in a hypothetical way) we would "get out" whatever gases are in that planet's atmosphere, would it be possible to create an environment in which we could breathe?
Short answer: yes.
Long answer: a breathable atmosphere is defined as an atmosphere were we can breathe, thus containing the gases we need to carry out this physiological process. This basically requires oxygen with a partial pressure of about 0.2 bar and no gases with a lethal effect on us. Since the buffer gases you are using are those commonly found in our atmosphere, this implies that the resulting atmosphere would be breathable.