Hello, I'm asking this question just to be sure that I know filtering enabled correctly. As this is a concept question, no scripts are needed.
Can a player change stuff in their own character in workspace through a local script and have it replicate to the server in filtering enabled? For example, if their was a value in my workspace player that was true and then I changed it to false, would it replicate to the server?
Please answer. I know the client controls their own movement so if that's what you were gonna answer, DON'T.
No, the only thing that will replicate are those parts that they have network ownership of (character by default), as you already mentioned. You could always test it with a local server in Studio if you're unsure.
Yes, the client can do whatever it wants to it's character. If there is a local part (part created with a localscript on a client) and the character jumps onto it, the character will appear to be flying.