Could you please tell me if these are correct?

1 Would leaving out the X give the sentence a different meaning?
2 Does not including the last bit make the meaning of the sentence different?

Thank you
They are both correct.

However sentence 2 : "does not including the last bit......" can be read as a negative question or a positive question. It might be better to use "does leaving out the last bit......." if this is what you want to say.
I agree with Louise. Try, "Does leaving out the last bit change the meaning of the sentence?" That sounds a bit more natural.