You can change the shape of the textures also, but it is limited since the photon effect in the game 'spins'. Even if the texture is changed to be non-rotational, it would still not keep the orientation that the Nemesis 'pulse' style torps would need. Or, at the least, be very troublesome in getting it to look decent.
An alternative would be to use a pulse effect since it is already set up to stay in the same direction and has a similar look and speed. In SFC3, the weapon damage amount can be altered so it could work at the expense of the original weapon. In the other SFC games, one could alter the Hellbore or the ESG Lance effect, though, again, at the expense of the original.