Eagles started out as a country-rock band with an emphasis on country, back in the Bernie Leadon/Randy Meisner era. Lots of fiddles, banjos, etc.
Then they picked up Joe Walsh and lost Leadon and Meisner, and became more of a rock band with Hotel California and The Long Run.
As much as I love “The Great Rock’n’Roll Swindle”, it wasn’t really a Sex Pistols album but a joke/fuck you from Malcom McLaren, who maybe wanted to test how much he could milk the Sex Pistols craze, even without a band.
(I love the symphonic pieces)
Very true-- they really did evolve lyrically from their ‘License to Ill’ days. I still listen to a lot of their stuff to this day-- "Ill Communication’ probably being my favorite Beastie album-- but a few years back I listened to ‘Liciense to Ill’ and it didn’t hold up at all to me as well as I thought it would. Still some great songs on that album, but some of the lyrics come across to me now as ridiculous and cartoonish. Like listening to these young New York children of privilege sing the lyrics to Rhymin’ and Stealin’. 
Thanks, amusing listen! I bet even my mom would approve…
The Doobie Brothers were a fine band until Michael McDonald songs took over. Then they sucked.
Seconded. If I ever hear another McDonald song again, I’m going to shove meat thermometers into my ears–pointy end first.
Hang on a tick. . . did I misread somewhere that Grace Slick and Paul Kantner were silent partners in Starship, silent only because they hated the ‘pop-py’ direction the band was going in, but loving the royalties checks?
Tripler
Hell, I switch the radio to ‘silent’ every time I hear ‘We Built this City…’
I’m going to make a terribly tasteless mention of Keith Relf of the Yardbirds, whose 1976 death by electrocution definitely involved a big transformation (a transfer of electrical energy from one circuit to another).
Well God, and their fanbase. 
They’re still touring, I’ve seen them twice in Denver since 2017. Their transformations have been more or less deliberate as their (at least Vanian’s) thoughts on their material is, “We’ve done that, why would we do it again?”
2 punk albums, 3 progressively darker Brit pop albums, 1 goth masterpiece, 1 more pop, 3 albums stuffed with absolute banger rock and roll tracks, and in 2018 an overtly political manifestation that sounds a bit like rocked-up mid-80s Moody Blues. Their last is not my favorite, but jesus they’re well into their 60s. They still prefer to play smallish venues for like $20 ticket. Just before the plague hit I was seated in a balcony maybe 20 feet from the stage. in 2018 my Missus accompanied me (she’s more of a Groban gal) more out of spousal support than interest I think. She was enthralled by Vanian’s voice–the old coot still has some gold in his pipes.
Hawkwind. Of course five decades and a small army of former personnel will change a band’s sound. Psychedelic Hippie, Space Rock, Heavy Metal, near-Punk, Electronic, Drone, and more are all part of Hawkwind’s music.
It’s…convoluted. At one time there was Starship AND Jefferson Starship in existence and touring. The wiki article barely scratches the surface.
Maybe also with mind altering drugs.
I thought that was the point. Wasn’t that all tongue-in-cheek?
Ignorance fought. More transformed than I realised.
I’m about the same age as the Beastie Boys. What seemed like tongue-in-cheek good fun to me in my early 20s now just seems kind of embarrassing, and apparently they agree, according to what @ZipperJJ said about their autobiographical documentary.
Same for me. I was 18 when “Licensed To Ill” came out and in the right age bracket to rock out to “You Gotta Fight For Your Right”. Then I somehow lost contact with the band, until I bought 1994’s “Ill Communication”. It still was a lot of fun, but I thought then that it was a much more mature work, like I had grown more mature in between.
Journey started out a jazz fusion/ prog rock band and became a pop rock back with ballads after Steve Perry joined the band.
Spinal Tap evolved from psychedelic pop into hard rock and then jazz fusion.
If we count the reversion from jazz to rock, which was professionally desirable in my opinion, that’s 3 transformations in total, making Tap the most metamorphosed and confused band ever to come out of the UK.
King Gizzard and the Lizard Wizard is a complete free for all stylistically who seem to change every album. One album could be metalish; another experiments with microtonal paychedelia; another goes for jazz. They are all over the place.
Van Halen went from Glam Rock/hair metal to a more Hard Rock/Blues Rock when they fired David Lee Roth and replaced him with Sammy Hagar.
In fact i believe this was the source of the “creative differences” that led to Roth being fired. Roth wanted to continue what they were doing and the others wanted to shift in the new direction.
Katatonia wąs a promising young doom/death metal band from Sweden in the 1990s; after a couple of albums vocalist and co-founder Jonas Renske developed problems with his vocal chords. The band simply switched gears a bit, found a comfortable place for his vocals to fit in, and kept on. Producing some incredible work over the next couple of deacdes, they are still a working band, releasing their 11th full length album back in 2020.
Here’s the song that instantly won me over: Soil’s Song from their 2006 album The Great Cold Distance:
Same could be said for Ween (well, not the microtonal): They have veered all over the place musically.
I’ll add in Meat Puppets. Their first album is fairly hardcore but they then shifted into psychedelic country rock…or something like that. They are hard to explain.
Do weird digressions count? I love Queen, and I have to say there wasn’t a ton of evolution in their sound from the first record to the last except better production and more keyboards in the 80s. But in the middle of it all is Hot Space, and almost unlistenable (to my ears) cruddy disco record. I own it because I’m a completist but holy crap is it a bizarre oddity. If not for containing “Under Pressure” as its final track, the disc would be utterly worthless.
There’s also the strange case of the Velvet Underground, who started as glorious droning pre-punk Warhol art trash, then got softer when John Cale and his viola were booted, then became a cool straightahead jamming band for Loaded and then there’s the U.K.-released album Squeeze which had no original members on it. Doug Yule, who’d been with the band since their third record, became the leader once Lou Reed and Sterling Morrison had hung it up. Here’s the bizarre thing: I’ve heard Squeeze and expected it to be terrible, but it’s actually quite listenable, if lacking in personality. Definitely not the Velvets, for sure. But I’m glad I found it after literally years of looking.