I think that the sniper has changed from a singularly driven individual whose purpose could be seen as fanatical to one who has embraced a sensitivity about his own role in the war's destruction and the need to stop it. When the reader first sees the sniper, there is an almost fanatical zeal about what the sniper is doing, described in instances where the sniper is "too excited to eat" or an individual whose own fanatic tendency is brought out in his eyes and the way in which he confronts death. There is a singularity and a type of one dimensional element to the sniper. He can be seen as fanatical because the sniper does not really contemplate the complexities that surround his being. There is a mission, a target, and a job that must be done for the Republican cause. Little else is present. Collateral damage appears and is perceived to be the necessary price of war. I think that the transformation comes with the accomplishment of his mission. There is no excitement at this particular point. Seeing the target hit, the transformation takes place:
The sniper looked at his enemy falling and he shuddered. The lust of battle died in him. He became bitten by remorse. The sweat stood out in beads on his forehead. Weakened by his wound and the long summer day of fasting and watching on the roof, he revolted from the sight of the shattered mass of his dead enemy. His teeth chattered, he began to gibber to himself, cursing the war, cursing himself, cursing everybody.
It's the accomplishment of the mission that causes the change within him. The moment that the sniper is able to see the results of what he has done, the consequences of his action, there is an emptiness evident. This emptiness and sense of the "shuddered" that falls upon the sniper is where his transformation begins. While he is a warrior and previously seen as a fanatic, it becomes clear that he is a child, filled with being "bitten by remorse." His cursing is a reflection of his own condition, one that would make him fanatical. It is this moment, the instant of accomplishment, that helps to establish the change and transformation within the sniper.