Function write_emote_key_to_project_dir 

pub fn write_emote_key_to_project_dir(
    project_dir: &Path,
    key: u32,
) -> Result<PathBuf>

Atomically add or replace emote_key in <project>/key.toml while preserving every unrelated line and comment in the existing file.

The DWORD is written in the conventional fixed-width hexadecimal form when the key is new. If an existing emote_key uses decimal notation, its radix is retained.