would it be wrong to clearly state the tangible differences in the newly defined 'races' then?

It's never wrong to acknowledge reality, but it would be wrong to use the word 'races', as it simply doesn't apply. Those would be new species. The reason to try to use the word there is because racism is recognized as bad because it involves discrimination based on differences irrelevant to character, while specisism is not necessarily.

And then act on it in a way that society deemed acceptable, even if it involved killing or mistreatment?

This has the same answer previously given: There's no reason to treat people as a group rather than individuals. If a new species that was an off-shoot of homo sapiens, or were aliens, or robots, or whatever, started attacking and killing us, then a violent response may be justified. If any individual in the group didn't do so, we shouldn't treat them as criminals. In practical warfare this could be hard to distinguish, but that's exactly what happens in real life among similar humans, without racism or specicism being involved.

How would this sit with your liberal ideals?

I honestly think your attempt to use this example has strayed too far from the point you were originally making to be useful. I mean if your point is that God stops you from being racist while science doesn't necessarily, you've heard unambiguously why there's scientific reasons racism is wrong, and now are stretching for "What is racism were true and accurate, then would you be racist? Because I wouldn't." That's not more moral or sensible. Racism is wrong, because it's factually inconsistent with ethical principals. If it were consistent, then denying that isn't a moral virtue.

There is no sky daddy in charge of any of this, evolution could have gone in any way

That's like saying if there's no sky daddy, gravity could go any which way. Evolution is a deterministic process. The factors are complex enough that it can be hard to predict, but biologists can rule things out, like how humans are not about to grow wings, or races are not about to become 'species'. If we did allow this could happen, then treating people based on the content of their character would be sensible regardless of their species or race.