Can clerics change their cantrips after a long rest?

Nope. When you’re preparing your spells after a long rest, you’re preparing things for which you have spell slots. Cantrips don’t use spell slots.

Is is too powerful to be able to? I mean, they are cantrips. I personally allow changing whenever they can depending on their class and never found it problematic 

If at all, I would say maybe on level up you could change, but down to the DM and what they allow.

Mechanically the classes do not allow it - as cantrips are spells you have cast so often you can just keep casting them taking minimal effect on you.

If you have players, especiall new ones that made a dreadful mistake with their choices, of course consider it.

If you allow changing cantrips every rest you are granting a ridiculous utility especially to sorcerers/bards they otherwise couldnt have, as once they pick spells they are locked in with only one change per class caster level allowed, so a firearms locker of cantrips doesnt make much sense. Under this consideration it is not too powerful but it discourages any consequence of build choices, ignores mechanics with the only attempt to justify it as 'why would it be bad?' and will prevent starting casters cantrip choices differentiate themselves from other casters. It also wont get to the root of the problem of why what they originally chose isnt working for them and allow one level dip characters access to every single cantrip of a class to choose from every short rest. Not cool.

I wouldn't like allowing changing on a long rest since they're supposed to be spells that you know so well that you're very good at them.  On the other hand, the permanent lock on them by RAW seems a bit much.  I'd suggest allowing swapping a single one on level up.

I have always allowed players to change their cantrip whenever they can change a prepared spell. Some exception I place on this are cantrip gained from a feat, Pact of the Tome, etc.

I am having to reconsider this now because one of the class abilities of the new Artificer, at 10th level, is to swap a cantrip on a short or long rest.

Up till now, with the Artificer, I've never had any issues with characters changing cantrips this way.

"Oh, hey! I just found a brand new cantrip but can never use it . . ."

I have gone by the change spells (cantrips included) at level up.  Generally I have been forgiving with the 1 change per level up but my players are still low level, and I have told them it will be more strict once they pass level 5.  I feel they should have a good idea about what they have liked so far at that point.

The issue with not being able to change cantrips is when you sub class or something that gives a cantrip you've already prepared a free slot. Now you have 2 of the same cantrips without the option of choosing another. Unfair in my book. I need to be able to have the option of choosing a new cantrip on my sheet.

This thread is over 3 years old and since then Tasha's has come out with an optional rule that you can change a cantrip when you level up to a level where you gain an ASI.

The only case I can think of where you get a new cantrip without a choice is a very limited number of subclasses (e.g. spores druid), I would expect most of the time when creating your character you would know what sub class they will be taking and plan accordingly but if not at least you can swap it out at level 4 (unless you delay it by multiclassing)

For me as a GM if something is giving you a cantrip you already have I would allow you to get a different one in its place like how backgrounds do with skill proficient.