For about the same weight of the historical 8x.303 armament they could have 1x20mm Hispano motor cannon, and 4x.303 in the wings. And since the early reliability issues of the Hispano were apprently largely due to wing flex and being mounted on the side to make the drum magazines fit, this wouldn't have been a problem with a motor gun installation. I think this armament would have a significantly better punch than the historical one, particularly against bombers.How much of a difference that would've made for, let's say, 1940?
As for what difference it would have made to the war, hard to say. RAF obviously won the BoB regardless, but with a punchier armament I guess they would have extracted a higher toll on the Luftwaffe, particularly bombers. Would that have led to Luftwaffe gritting their teeth and eating up higher losses, or would they have given up on BoB sooner, hard to say.