Yes, the important words should sound similar, from what I learned listening to Weird Al do it. Like a virgin becomes like a surgeon.
Then there should be a silly theme. The more mundane the subject matter, the better it is as a novelty, IMVHO. I don't think about any of this formally, just something I've done ever since I heard "Another one rides the bus." Used to play pinochle with a guy who could rip off alternative lyrics instantly to anything on the radio. He'd have us laughing so hard we couldn't play.
Most of the alternative lyrics I've written over the years weren't about plants, but there's not much audience for those. My family is rarely as amused as I am. IDK why, but they don't care about U2's "Where the sheets have no stain", Beatles "She's got a chicken to ride", CCR's "There's a bathroom on the right", I don't know who sung "Secret Asian Man," and I don't blame my husband for not appreciating Miley Cyrus "It's the grime" (which is about needing to take a shower.) I think my best one is Eagles, "Gonna be a fruitcake tonight." Maybe I'll put it here at the end of the year. Fruit is plants, right?
