Can during deacceleration all energy be absorbed and used for accelerating at a later moment?
If we will ever have the technology to instead create proper massive particles at scale you could eject those in orbit around some other massive object and then re-steal their angular momentum to accelerate yourself. But that I believe would be an extremely lossy process so you would lose most of the energy.
now, the question of how to design an actual working solution? i don't know; and basically, it depends. you would then also have the problem of whether it was possible to implememnt that solution, using real matter and physical objects...
unfortunately, that was probably the question you really wanted answered, right?