Changing perspectives?

Yes, it has been done before. Uh... all I can think about right now is a book that's called El Barco de la Ilusión. You get the first person narrative from the protag and then you get the third person narration from a MS a secondary character is writing.

LOL, I asked the same thing earlier this week. Seems that there are a few daredevils around these parts!

Good luck with your project!

If you're unpublished, I personally think this is a big ask for an agent or publisher to be taking a risk with your story. For a first book, I would consider sticking to the one POV. There are plenty of examples of this being done as you have described, but I suggest these are, in the main, from established authors with forgiving readers.

JJ

If you are writing in first person for the main character, there's really no choice but to write in third for the remaining characters. Having more than one first person POV would be a problem. As long as you "indent" the journal entries, which I assume are first person. I'd say do what feels the best for the work you are doing.

House of Leaves by Mark Danielewski. It was his first book. i'd say it was a work of genius, not just a mere novel. i think a book has to really be a grand slam to make it work. The POV is all over the place-scraps of paper in a trunk, scholarly articles, crazy people's memoirs, 1st person.

If you like it, and you find your Beta Readers like it (When you get to that point), then go for it.

It's like food, it's not how you get there, it's whether it tastes good that matters.

This scenario can be done effectively and has been done effectively in the past but, as a reader, I have to say that I'm not a big fan of various forms of perspective in a single story. Jumping from first person perspective between two or three characters in a book is one thing but when you're jumping between first person and third person and journals etc it'd be awfully complicated (not to mention jarring) and you risk completely confusing the reader. As one of my writing teachers told me: "A confused reader is not a happy reader."

The Bartimaeus Trilogy by Jonathan Stroud uses this technique well. Some is told first-person through Bartimaeus' eyes, then the rest is told third-person limited from Nathaniels POV, then later third-person limited from Kitty's POV.
Great book, and it wasn't at all confusing.
I think, so long as you only have one first person character, it should work fine. Two first person POVs might be a little confusing... (lol I'm the exact opposite here to Patrick)

It has been done

If I'm not mistaken, this was a popular approach of modernist writers (maybe post modernist?). William Faulkner in particular was very fond of using this technique in his novels, some of which include The Sound and the Fury, As I Lay Dying, A Light in August, and Go Down, Moses.

You shouldn't really be concerned with whether other writers have done it successfully before, you should be concerned with why you're doing it. My advice would be not to do it unnecessarily. Doing it just to be different isn't a good enough reason, especially considering that it's been done since the beginning of the 1900s. The Modernists were trying to present the idea of an unreliable narrator, challenging a reading audience that always accepted the speakers word as complete truth. By using multiple narrators, they were trying to show that everyone will give different accounts of the same situation, even if they think its true, so you can never accept one persons story as factual.

So I think you need to answer the question, why are you using multiple narrators? If you have a good reason, then you'll find your story will be more successful.

I believe the Boleyn Inheritance by Phillipa Gregory is a good example of this.

As long as each voice is distinctive, you should be fine