I'm a quitter. I come from a long line of quitters. It's amazing I'm here at all.
I can feel bits of my brain falling away like wet cake.
No: any dice that you do not roll are locked. What you're really doing is locking (setting aside/making inactive) at least one die. Of those 6 dice, you could lock 1 or more than 1.
What you can't do is "semi-lock" some dice. You can say "Okay, I've rolled 6 dice, I'm setting aside this " but you can't then say "...and I'm not going to reroll these s this time... but maybe I will reroll them next time, depending on what I get."
If you're not rerolling it, it's no longer active.