Is it okay if the location of "ever" is changed?
Yes, you are correct in assuming the position of "ever" can be changed. Instead of "best boss we're ever gonna have," the "ever" can be moved to the end of the sentence to create "best boss we're gonna have, ever" without changing the meaning of the sentence. However, this requires the use of punctuation to break up the sentence, so "ever" in its original position is still the most natural way of using the adverb. When used to mean "at any time," "ever" should come before the main verb or subject. Ex: This is the best cake ever. Ex: What is the most beautiful place you've ever visited?