If you are using an extension that includes a conversation system, there might already be a way to refer to all talking-related actions--you could check the extension's documentation to find out.
If not, you could create a kind of action that includes the different talking-related actions. See ยง7.15. Kinds of action in the manual.
If you use the ACTIONS command and type "Computer, hello", it seems to fall under the "answering it that" action, so that should be included.
You could make a kind of action that's specific to this computer:
Asking the computer about something is fruitlessly dialoguing.
Telling the computer about something is fruitlessly dialoguing.
Answering the computer that something is fruitlessly dialoguing.
Instead of fruitlessly dialoguing:
say "'Voice print not recognised.'"
If there are any other talking-related actions you want to include (see "Actions" in the Index tab), you can follow the same pattern.
Or if you want to be able to write rules that apply to all talking actions that are addressed to a particular thing/person, even if the action is not addressed to the computer:
Asking something about something is dialoguing.
Telling something about something is dialoguing.
Answering something that something is dialoguing.
Instead of dialoguing when the noun is the computer:
say "'Voice print not recognised.'"