In my CF town, I always make their catchphrase "beasley" and I make the greeting "Oy you".

"Oy you! It's crazy cold today... Oh, hey, We may get a glimpse of you-know-what! When the sun goes down, strap on your cold-weather gear and watch the night sky, greenhorn!"

-Ed

I always make their greeting "Hi".

But for Merry I made her say "sparkles" because she wanted a sparkly greeting.

As for catchphrases, I just leave it how it is, although I got Pecan to say "écureuil" (French for squirrel).

I am not very creative.

No. The only rule is that their catchphrase/greeting is mostly a pun or a reference (for example, Whitney's greeting was once "Canis day end?" and Rudy's catchphrase was once "meowntain"; I have a poor sense of humor, I know)

Every one says "howdy" and I try to keep them saying their normal set catchphrases.

I made Cherry's Catchphrase li'l bro, and I made Chadder's greeting Let's chat, mon amiè.

I gave one of them "Hot Mess" as a catch phase when we first started......  each Villager uses it, along with other ones that we change when they ask.  But, they ask each of us if they should change "Hot Mess" and we always always say no.  They ask 2X a week, each Villager to each player (3 of us).  

My (adult) daughter tends to give them nasty sayings, using the other language letters to get it thru the filters.  

Generally I'll use "Allons-y!" as a greeting ("let's go" in French, and it was also the Tenth Doctor's catchphrase), but when it comes to catchphrases, I either keep it the same if it's one that I'm particularly fond of, or I'll put something adorable or something that fits the animal type/personality/look.

I have Astrid say Beep bop as a catchphrase.

I’m new here.

Blanche: Banana bread
Patty: Moo
Buck: Giddy up

One time, Curlos’ catchphase was “shearly”. When Stitches came to him, Stitches changed HIS catchphase to the same exact one.

The reason why I added Fang is because I'm gonna replace Tex with him when Tex moves out.


JJBA Greetings:

Antonio: Yare yare daze (Jotaro Kujo)
Freya: Yare yare dawa (Jolyne Cujoh)
Alfonso: Za hando (Okuyasu Nijimura)


JJBA Catchphrases:
Sheldon: ooooh noooooo (Joseph Joestar (Part 3 Japanese dub))
Alfonso: bro (Okuyasu Nijimura)

Planned JJBA Greetings:
Apple: Volare via (Narancia Ghirga)
Whitney: Spice girrrrl (Trish Una)
Carrie: But I refuse (Rohan Kishibe)
Sheldon: Oooh myyy goood (Joseph Joestar (Part 3 JP dub))
Diana: Surprise, I'm a fake (Mannish Boy)
Fang: Bravo, bravo (Jean Pierre Polnareff)

Planned JJBA catchphrases:
Freya: stone free (Jolyne Cujoh)
Antonio: ora (Jotaro Kujo)
Whitney: wannabe (Trish Una)
Carrie: heaven's door (Rohan Kishibe)
Diana: lali-ho (Mannish Boy)
Apple: aerosmith (Narancia Ghirga)
Fang: silver chariot (Jean Pierre Polnareff)

For greetings, it's always just 'hi' 'hiya'

catchphrases however are completely random and whatever pops into my head first. Lately it's been fruit.

Maple: Hey honeybee! I was just thinking about how nice it'd be to see you, pear.

I can't remember many changes, but on New Leaf I gave Bunnie the catchphrase of DinoThundr [extend the limit in the Switch games please], and it stuck. She's never asked for a replacement and has never changed it.
Maybe its her favourite as it is mine. Who knew Power Rangers existed in the Animal Crossing universe?

I usually stick with their standard/default catchphrases if I think it suits them best (i.e. Francine - "karat"). I made Octavian's catchphrase "peasant" and it's great. xD

During football season, I get as many villagers to say #OnePride as possible - it's the Detroit Lions' hashtag.

I'm also fond of making them say bad words, but nothing nasty, just silly. Or I try to think of a pun that relates to the type of animal they are - Astrid the kangaroo currently says BOING! and Lionel the lion says RAWRRRR.

For greetings, since they only say it to me, I try to make it something that will make me giggle. Elmer is my favorite, so he says OMG, HI BFF! Boris wanted something that made him seem nicer, so he says Rainbows&Smiles!

I give all of my CF villagers catchphrases that match names of characters from my favorite book series. These include Theodora (Buck), Moxie (Bob), and Ellington (Gaston). Whoever knows what book series these three characters come from gets (imaginary) bonus points.
As for greetings, I tend to say hello in other languages. Sometimes these are more common (Bonjour or Hola), but sometimes they're more unique - one character says hello in Pig Latin, and another says hello in a language my sister invented.

I made Zucker's catchphrase 'otako' a portmanteau of 'otaku' and 'tako', which means octopus in Japanese

I used to make it a variation of their previous catchphrase in New Leaf but I just make it into little jokes like I made Inkwell's catchphrase "woomy" when he was at my town. For greetings, it was just the boring old "hello" but now it's the same situation as the catchphrase like I made Punchy's greetings "hoi".

I gave Jitters a catchphrase of "fibit" because he's sporty and now everyone is saying it

I recently changed Hamlet's catchphrase from "hammie" to "hamigo." He liked it, but the thing is that the rest of my Villagers seem to like it too...It went viral, and now EVERYBODY's saying "hamigo"!

I have no real set rule to it, but almost all my edited villager catchphrases have some kind of meme reference to it, for example, Croque says "else if", which is a line of code that well-known developer YandereDev consistently abuses. Chalice moment.

Mine say hello in certain ways depending on their personality.
Basically, like this:
Velma and Miranda: Hello there.
Peck: Wassup?
Chadder and Colton: Hiya!
Chrissy: Hiya! also
Deli: Hihi!
Gaston: You again
Pashmina: Heyooo!

Forgot Annalisa in my old post. she says good day.

Most of mine say “SHOOT THE PUCK!” as I have an ice-hockey rink on my island!