Does jumping in YHTWTG make your horizontal move speed change?
Nope, the horizontal movement speed never changes. It correlates 1:1 to the input device. It doesn't change when you're jumping, and there's also no ramp-up when you start moving or ramp-down when you stop moving. That was a conscious decision made to help facilitate precise platforming and largely influenced by the Mega Man series, which has historically done the same.
Super Win the Game maintains this behavior in most cases. The two exceptions are when you're walking on ice or swimming. There's lots of ramp-up and ramp-down applied for icy surfaces (although it still doesn't change your speed while jumping), and you walk slower but jump higher underwater, again hearkening back to Mega Man.