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Indeed, the conversion between some subatomic particles, such as the decay from neutron to proton, is caused by the weak force. But I don't think this is related to Bose-Einstein condensation (BEC). BEC is a collective behavior of many particles together, while the conversion between the subatomic particles occurs at a single (or few) particle level.

I'm not sure what you mean by the changing of subatomic particles into another subatomic particle. Is there a specific phenomena you are referring to, or do you mean it hypothetically?

The Bose-Einstein condensate is a state of matter that forms when gasses of Boson particles are cooled down to near absolute zero temperatures. The new state of matter forms because at low temperatures, the Boson particles all occupy the lowest quantum state. Due to the wave-like properties of particles, all the Boson particles with the same quantum state will interact and form a collective wave. This collective wave is the Bose-Einstein condensate.

The criteria for being considered a Boson is if the particle has an integer spin. These Boson particles can be subatomic, but there are also composite particle Bosons, which are not subatomic. The Bose-Einstein condensate has only been observed experimentally for these larger composite Bosons. Some examples of this include Helium-4 and Rubidium-87. So I don't think changing a subatomic particle would be an example of the Bose-Einstein condensate. Hope this helps!