How can I insert new candidates to already open minibuffer?

[wybryk-ananasa]

I would like to insert new candidates into already open buffer.
How can I do it?

[minad]

This question is out of scope/too generic for the Vertico discussion board. I suggest to read the documentation of the completion mechanism, see https://www.gnu.org/software/emacs/manual/html_node/elisp/Completion.html. You can create your own custom completion table (which stores the candidates as a list for example) and implement separate commands which add to this list.