So, you can't change it via mods because "core" is "protected" although you change it manually.
Like (from main folder game\data\core\prototypes\utility-sprites.lua):
health_bar_green_pip =
{
filename = "__core__/graphics/health-bar-pips.png",
priority = "extra-high-no-scale",
width = 7,
height = 7
},
health_bar_yellow_pip =
{
filename = "__core__/graphics/health-bar-pips.png",
priority = "extra-high-no-scale",
width = 7,
height = 7,
x = 7
},
health_bar_red_pip =
{
filename = "__core__/graphics/health-bar-pips.png",
priority = "extra-high-no-scale",
width = 7,
height = 7,
x = 14
},
ghost_bar_pip =
{
filename = "__core__/graphics/health-bar-pips.png",
priority = "extra-high-no-scale",
width = 7,
height = 7,
x = 21
},
bar_gray_pip =
{
filename = "__core__/graphics/health-bar-pips.png",
priority = "extra-high-no-scale",
width = 7,
height = 7,
x = 28
},
shield_bar_pip =
{
filename = "__core__/graphics/health-bar-pips.png",
priority = "extra-high-no-scale",
width = 7,
height = 7,
x = 35
},
Into:
health_bar_green_pip =
{
filename = "__core or your mod__/graphics/invisbile-pips.png",
priority = "extra-high-no-scale",
width = 7,
height = 7
},
health_bar_yellow_pip =
{
filename = "__core or your mod__/graphics/invisbile-pips.png",
priority = "extra-high-no-scale",
width = 7,
height = 7,
x = 7
},
health_bar_red_pip =
{
filename = "__core or your mod__/graphics/invisbile-pips.png",
priority = "extra-high-no-scale",
width = 7,
height = 7,
x = 14
},
ghost_bar_pip =
{
filename = "__core or your mod__/graphics/invisbile-pips.png",
priority = "extra-high-no-scale",
width = 7,
height = 7,
x = 21
},
bar_gray_pip =
{
filename = "__core__/graphics/invisbile-pips.png",
priority = "extra-high-no-scale",
width = 7,
height = 7,
x = 28
},
shield_bar_pip =
{
filename = "__core or your mod__/graphics/invisbile-pips.png",
priority = "extra-high-no-scale",
width = 7,
height = 7,
x = 35
},
And you need to create "invisbile-pips.png" as a fully transparent image.