Changing publishers in mid-series

Is doing this a good idea? Are there any legal ramifications?

I'll be waiting for an answer to that with you, Richard. I don't see a
legal problem unless you made a series part of the contract. I have a
sequel ready and may choose a different publisher.

Charlene Baumbich who wrote the Dearest Dorothy series was in the middle of her 7th book in the series when she learned from Penquin they were not going to pick her up. She could have fielded out the 8th in the series to a new publisher. She chose instead to go into non-fiction.

So I guess in answer to your question, yes would be the answer. (That sentence doesn't sound right.) Anyway, yes you can go with whomever you chose unless, like Brew said, you made the series a part of the contract. Or you are tied into your publisher in another way: say, you have to write so many books for them or something like that.

On the other hand, many mystery series have been released by more than one publisher. Check Lawrence Block's various series for an example. There are many others. The reading public doesn't give a hoot about the publisher. If asked about a particular series or even a single book, how often could you say it was published by . . .
The one downside would come if a writer was accustomed to working with a single editor at a publishing house, but that should be easily overcome.

Authors change publishers in mid series all the time, for various reasons.

It's actually a way bad idea from everybody's standpoint.

But it gets done and for strong reasons. Not getting the next book picked up is a pretty obvious and compelling reason.

If the new publisher is willing to do it, why not? They are the ones to whose disadvantage it is, essentially promoting a series whose sales benefit another publisher.

The writer obviously wouldn't switch except for reasons of advantage, so it's obviously cool from that viewpoint.

There is a danger in a writer having work spread out over a lot of publishers: it ends up that nobody is willing to really get behind the brand. But if you get dumped, what else are you going to do.
Or if you get offered a lot more money, what else are you going to do but take it?

I have found much wisdom and courage here, and I thank you all. I think that I have a lot to think about while writing number four. Much stuff is on my mind now.