I just realized that my request was poorly expressed now that I have discovered the functions "save and load" in the manual. I did not know this feature because my research on saving system led me to the webstorage, then to the localstorage.
So my request changes: it would be exactly the same function as adding "save and load" but for specific objects - by name - as arrays, variable etc.
In fact, I even wonder why it does not already exist in official functions.
In my dreams I see a variable whose value changes all time an ennemy is destroyed... then I see inserts in the event sheet, simple, basic, open to the most ignorant game creator:
on layout start > load "higscoreVariable" from "mySaveSlot"
on player destroyed > save "higscoreVariable" to "mySaveSlot"
I smile at the mere idea of the size of tutorial about this kind of storage system