You can do it ondeath checking if player has X storage (bless) then setLossPercent.
Im on the phone, on home I try put a script.
Here:
function onDie(cid)
-- Add this
if getPlayerStorageValue(cid,6000) == 1 then -- (or your bless function checks)
doPlayerSetLossPercent(cid, 0, percent) -- I dont remember exactly id of exp and skills, but test it.
setPlayerStorageValue(cid,6000, -1) -- (or your bless function checks)
end
-- Add this on npc bless seller when players buy it
setPlayerStorageValue(cid,6000, 1) -- (or your bless function checks)
doPlayerSetLossPercent(cid, 0, percent)
doPlayerSetLossPercent(cid, 1, 0)
When player buy it and die then lose just that you add on this lines
and then when dies checks if it has the bless and then remove that.