right click hades on steam > manage > browse local files > content > scripts

open HeroData.lua with any text editor then
set MaxHealth = 200 or 500 or 5000 or whatever
save the file

open MetaUpgradeData.lua aka the mirror of night with any text editor then
set StaminaMetaUpgrade aka greater reflex dash set all CostTable to 0
set ExtraChanceMetaUpgrade aka death defiance set all CostTable to 0
or set all Cost and CostTable to 0 and UnlockCost to 0 (but when i tried this not all are working on the mirror of night)
save the file

open StoreData.lua aka wretched broker with any text editor then
set all CostAmount to 0
save the file
some guides on the keywords
MetaPoints aka darkness
Gems aka gemstone
LockKeys aka chthonic key
GiftPoints aka nectar
SuperGems aka diamond
SuperGiftPoints aka ambrosia
SuperLockKeys aka titan blood

alternatively before a fresh save on hell mode open HeroData.lua first with any text editor then find HardModeStartingResources
delete the double hyphen signs in front of MetaPoints, Gems, LockKeys and you can change the number values if you want
here is how it looks like originally
HardModeStartingResources =
{
--MetaPoints = 2500,
--Gems = 500,
--LockKeys = 10,
}
save the HeroData.lua file then choose hell mode on a fresh save slot

to reset all the modification of lua scripts at once just right click hades on steam > properties > installed files > verify integrity of game files
and then steam will redownload and replace the edited lua scripts with the original lua scripts