A "position" is an opinion. Often it means a formalized opinion, possibly written and more or less permanent. It may be a stated reason for a "policy." For example, "we are discontinuing our lifetime satisfaction guarantee. Our position is that too many customers were abusing the guarantee, and incurring costs that had to be borne by other customers." "Once and for all" means "starting now" (once), "and continuing forever (for all), with no more changes." If the company needs to decide something once and for all, it suggests than in the past what there have been changing, inconsistent positions. One day one thing, another day another thing. The phrase suggests irritation and impatience. It suggests that the company has repeatedly taken a position, but has never stuck to it. "We need to stop doing this over and over. We need to take one firm, carefully decided position and then not change it again. We need to decide this once and for all."