At the bottom of util.lua there's a bit for controlling the health display - 
if CLIENT then
   local healthcolors = {
      healthy = Color(0,255,0,255),
      hurt    = Color(170,230,10,255),
      wounded = Color(230,215,10,255),
      badwound= Color(255,140,0,255),
      death   = Color(255,0,0,255)
   };
   function util.HealthToString(health)
      if health > 90 then
         return "hp_healthy", healthcolors.healthy
      elseif health > 70 then
         return "hp_hurt", healthcolors.hurt
      elseif health > 45 then
         return "hp_wounded", healthcolors.wounded
      elseif health > 20 then
         return "hp_badwnd", healthcolors.badwound
      else
         return "hp_death", healthcolors.death
      end
   end
You could put your own statement in there to, say, check if they are using a certain item or something then just return healthy.
For example :
   function util.HealthToString(health)
     
       if HPChanger == true then
         return "hp_healthy", healthcolors.healthy
      elseif health > 90 then
         return "hp_healthy", healthcolors.healthy
      elseif health > 70 then
         return "hp_hurt", healthcolors.hurt
      elseif health > 45 then
         return "hp_wounded", healthcolors.wounded
      elseif health > 20 then
         return "hp_badwnd", healthcolors.badwound
      else
         return "hp_death", healthcolors.death
      end
   end
Obviously HPChanger isnt a real variable in this case, but you'd put whatever you wanted in there to check.
Hope that helps.