It's in the issues on the github for the save editor.
You can set it past the games "max", visually it won't show... but its changed..
If your save is the latest save.. 1.5 on switch.. search for these values.. immediately the 4 bytes after are the values.. if you set it to FF or 255 it'll give you many hearts in game.. it will only show the max 27/30... but it's there.. for stamina it's the same thing, but it's in FLOAT value..
for example, I have my hearts set to 255 and stamina set to 6000.00 (max default is 3000- 0x45bb8000 ), in game if i get hit.. visually until i get low.. no hearts are decreased.. same for stamina.
MaxHartValue=0x27f30629
CurrentHart=0x93c99bbe
StaminaMax=0x47f0df3a
StaminaCurrentMax=0xac5eaf58