Function set_byte 

pub fn set_byte(
    bytes: &[u8],
    n: i32,
    value: i32,
    writer: &mut impl Write,
) -> Result<()>

Sets n’th byte in binary string to newvalue.

Example

query T
SELECT set_byte('\x1234567890'::bytea, 4, 64);
----
\x1234567840