Can I choose which stat to use?

Vincent, I'd like to play the rules as written before I start hacking it, but some of the wording is ambiguous.

The Angel move Professional compassion says "you can choose to roll+sharp instead of roll+Hx when you help someone..." while the move Sixth sense says "when you open your brain to the world's psychic maelstrom, roll+sharp instead of roll+weird" (no hint of choose there).

Does that mean I can't ever roll+weird for the psychic maelstrom? Does that move always come into effect because I am opening my brain?

Or is it a case of to do it, you have to do it, and dependent on me using some sort of sixth sense in the fiction, and if, for example, a machine opens my brain and projects the psychic maelstrom into it, I would roll+weird?

Can I choose whether or not to use Sixth sense as I see fit?

Is there a concrete answer or am I (we) supposed to decide during play?

If you aren't Vincent: I just want to know what the text means, I don't need suggestions on what I should do.

Thanks.

The moves that I designed to be optional say so in the text. Professional compassion, for example. The ones that don't say so in the text, I didn't design to be optional. Without going back to check, I think that the optional ones all involve Hx.

In a game so accommodating to customization, rewriting all the "roll+x instead of roll+y" moves to "you can choose to roll+x instead of roll+y" shouldn't cause you any problems at all, but if you want to play it exactly as I designed it, most of them aren't optional.

-Vincent

Cool, thanks.