Photon annihilation energy and particle characteristics at the speed of light ...?

We know that the photon is its own matter-antimatter (electron - positron) pair. Any thoughts on what might happen if it were actually possible to regulate the rate of electron - position annihilation, in a similar fashion as to how critical mass is regulated in a nuclear fusion reaction? By carefully controlling fusion in nuclear reactions, useful energy is created. By analogy, if electron - positron annihilation could be controlled in a similar fashion, might the photon be made to slow down and take on the characteristics of either the electron or the positron (or some combination of both), including their charge and spin? What I am talking about is a "controlled" electron-positron annihilation that might give the photon new heavier particle characteristics.

Best regards