“Doesn’t this change the meaning of the statement so much that it’s no longer true that every citizen of age who is a resident is eligible to vote?”

yep, especially in a country like the US where gerrymandering is still legal.

“Can this new language be interpreted by courts and lawmakers such that anyone can be disenfranchised if such malicious laws can be passed in the state?”

oh yeah, this can handily accelerate voter suppression.