Ok, does this work or fall into the killing cold scenario?

Cannot is absolute and reigns supreme, so no, Wittin cannot be damaged by Spice Visions while it's committed to the Force.

So can you still use spice visions since it says damage a character instead of focus him. Does that mean since u can do as instructed the event is nullified?

Sorry, not sure how/if the question is different from that originally asked in the OP, so don't know how to answer differently. If a committed Witten is focused, you can't change that focus into a damage using SV, because Witten "cannot be damaged".

The confusion is coming from wondering whether or not Witten can ignore the focus token even if he's not damaged.

No. He cannot use spice visions so he will be focused and not damaged.