diseases.lua

minetest.hud_replace_builtin("health", {
        hud_elem_type = "statbar",
        position = {x = 0.5, y = 1},
        text = "poisonous_heart.png",
        number = 20,
        direction = 0,
        size = {x = 24, y = 24},
        offset = {x = (-10*24)-25, y = -(48 + 24 + 16)}
    })

P.S: the table_definition is SAME it is written in statbar.lua file in builtin folder, only i`ve changed name of "text" element.