The scenario you described, where an up quark decays into a down quark, a positron, and a neutrino, and then the down quark decays into an up quark, an electron, and a neutrino, does not occur in particle physics. Quarks do not spontaneously decay into different flavors of quarks.
Quarks are elementary particles that are considered to be fundamental and indivisible within the current understanding of particle physics. They are bound together by the strong nuclear force, and changing the flavor of a quark requires the exchange of a W boson, which mediates the weak nuclear force.
Quark flavor-changing processes, such as up quark to down quark transitions, can occur through weak interactions, which involve the exchange of W bosons. However, these processes have specific conservation rules that must be obeyed. For example, in the case of quark flavor-changing neutral currents, the transition must conserve electric charge, baryon number, and lepton number.
In particle interactions, energy and momentum must be conserved. In the case of a particle decay or interaction, the total energy before and after the process remains the same. However, the energy can be redistributed among the decay products. The conservation of energy and momentum ensures that the total energy is conserved.
It's important to note that particle physics phenomena can be quite complex and are described by quantum field theories. The specific details of particle interactions, including conservation rules and energy-momentum considerations, are described mathematically through these theories.