If an ability would prevent Scorch from receiving a stress token by replacing it with something else, he still gets to roll an extra dice right? It doesn’t say “gain a stress. If you do...”.

Full text: "While you perform a primary attack, if you are not stressed, you may gain 1 stress token to roll 1 additional attack die."

My first inclination is to say no, you don't get an extra die. It looks pretty similar to other replacement effects related to cost paying. I'm pretty persuadable, but someone would have to cite rules and card texts and such.

no, you wouldn't get the extra dice. It specifically states a focus stress token.

Compare it to Jyn where you perform a focus action but you end up with an Evade token.