brunopalermo is right, if you simply need to set different values for two variables, event groups is a huge overkill.
If you don't like his solution, just create one variable Difficulty and a function SetDifficulty:
if Difficulty=1 : set life=50, lifeMax=50
else if Difficulty=2 : set life=100, lifeMax=100
else if Difficulty=3 : set life=200, lifeMax=200
When player chooses game difficulty, set the variable, write it to local storage and call this function.
On start of layout read this variable from local storage and call the function:
On start of layout
Local storage get "difficulty"
System wait for previous action
set Difficulty=max(1, LocalStorage.ItemValue)