Can you add to/change the code assist options?

May have already been answered if so please point me to it. Is there a way to add to the code assist window for options that don’t appear to be in there?

For instance TRUNC, if I want to type select trunc(some_column), SELECT pops up but TRU only pops up truncate_pool_track… which I’ve never used, but do use TRUNC all the time.