Polishing the piston cannot return missing metal - it can only remove more metal to give a smooth surface. When you finish polishing, the piston no longer fits the bore. Depending how much clearance it has, it may not seal the ports properly - it will rattle around, and may not happen to be close to the port's surface at the crucial time.
The short answer is, if it is really shallow scoring, you may get away with it or you may not. If the scoring has any depth, removing metal may make it work worse rather than better. Besides that, increasing the piston to bore clearance will make the piston rattle (a noise known as piston slap). So, give it a try if you want, but unless the damage is superficial and the engine still runs properly before you start, you will probably be disappointed.
