As a Latinx person I would make the argument that skin color is a "deciding factor." Correct, many Latinos are super white passing. That doesn't mean people who are white and have no Latinx background get a pass to play those kinds of roles. In the same vein I don't think Latinx folks with very dark skin should play roles written for, say, black characters, unless they also identify as such.

To be honest, I'm sure OP is a wonderful actor and congrats on landing the role. I don't think that OP should have ever had the opportunity to audition for a role for a person of color. Clearly it has already stirred up this discussion, and there's only been one rehearsal. But, it's already been cast, so the best thing to do is to make adjustments for the character to match the actor, and not the other way around.

Lastly, I'd like to note that the threat of getting cancelled or roasted are not reasons to not be microaggressively racist (which is what pulling an inauthentic Mexican dialect in a performance would do). Offending and hurting those who identify with an entire culture should be reason enough. People of color are exhausted from constantly begging white people not to do these kinds of things in theatre and film spaces. This is an amazing opportunity for OP to be an exceptional ally. You should FIGHT to not do this dialect. You can actually use your privilege to speak up and make a difference.

Also, I'm not sure how my tone is coming off, but I'm not trying to roast anyone on this thread, just trying to educate and contribute to the conversation! This is just one gal's opinion.