Is 은 and 는 interchangeable depending on whether the noun ends in a consonant or vowel?
Yeah, you use 은 after a noun ending in a consonant and 는 after a noun ending in a vowel.
마이클은 고기를 먹어요. - Michael eats meat.
니키는 야채를 먹어요. - Nikki eats vegetables.
(I'm not a native or fluent Korean speaker/reader, but I've been studying it for over a year and this is my understanding of it. I suggest you check out Talk To Me In Korean Level 1 Lesson 9 (available free online) cause it goes over the use of topic and subject marking particles!)