Sure it would release energy, but it would be less then the amount of energy that you used to fuse it together. The whole thing would need a massive source of energy which you could just as easily use to blow the stuff up in the first place instead of using it to power a generator to power the accelerator to smash the atoms to get the stuff to fuse (which may not even be possible) then somehow move it to the place of the explosion in a very very very very brief timeframe, while maintaining target accuracy and decelerating it at the explosion site. All these steps would require big bulky equipment very near the scene of the explosion, and all this equipmant must be powered in a fraction of a second with much more energy then released in the explosion without blowing up the ship itself.
The idea is stupid, even if you could get plutonium to fuse (which you likely can't) it would require much more energy then it releases.