Function splice_entries 

pub fn splice_entries(
    entries: &[Map<String, Value>],
    insert_after_seq: i64,
    new_entries: &[Map<String, Value>],
    section_override: Option<&str>,
    scene_override: Option<&str>,
) -> Result<Vec<Map<String, Value>>, String>

Insert new_entries after insert_after_seq, then renumber the body.

Preamble entries (seq <= 0) are never renumbered. New entries inherit section and scene from the insertion point unless overridden.