Using Save Wizard for Witcher 3, it is best to level to 100 before editing your stats because each time you level up, Vitality will reset to normal.
To change Vitality, search in float and change both sets to the exact values (XX XX XX XX, XX XX XX XX = F0 23 74 49 for 999,999). Now the tricky part is keeping the health because you want to change either Vitality regeneration outside of combat or during combat, which is difficult to find because it is set at 1 in float I believe
As for Stamina, I played around with the values and changed it to 9999, then managed to change a few float values valued at 1 to get 9999 for stamina regeneration