Not clear what you mean but I'll try:
A rocket is at rest in our frame of reference in space:
The rocket starts the engine. It uses internal combustion of fuel. The combustion causes expansion of hot gases. The expansion causes pressure in the engine resulting in forces that accelerate the gases in the only way possible; out to the left. The gases have momentum P. The force accelerating the gases causes a counterforce on the rocket. The rocket gains momentum P to the right. Center of mass of the complete system gases+rocket is not moved. Total momentum is conserved P-P=0.
The rocket shuts down the engine and moves at constant speed in our frame of reference. Gasses continue to the left. The center of mass has not moved. Total momentum is conserved P-P=0
Now we try to do an invention, let's put the rocket in a bubble and use a collector to gather the exhaust gases and use a machine to generate fuel from the vapour. Will the invention work? The combustion C is still internal in the rocket, exactly as above? The forces from the vapour will be the same, acting on the rocket? But as I have said a few times, conservation of momentum can't be beaten. The double will not move its center of mass. Now no mass can leave the system. The collector will have to stop the vapours. The forces required balances the momentum P of the gases. At best there will be some wobble while masses are moved around. There will be a lot of internal stress on the components, none of those forces will have any impact on the center of mass of the complete system, the bubble, the rocket, the gasses in motion etc.
Note that if we instead of vapour use photons it does not matter. You can't beat conservation of momentum.