It does not seem that there is a way to change the data. I tried:

$(...).autocomplete('setData', { data: newArray })

And that didn't work. If I flush the cache. it stops working altogether (nothing ever matched again)

There is already an enhancement request to get the data using a function, that would also do what I need.

My use case is to use it to pick from a list, but clear the input on selection. I don't want to show that option any more. (Basically it is the multiple selection but I don't want the full list in the input element)