What does the use of the word extralegally in paragraph 5 indicate about colonial activities in the period before the American Revolution?

The prefix extra - means "outside" or "beyond."

Therefore, when colonial activities are described as being "extralegal," that means the activities were outside or beyond the law. This means that their activities were not regulated by the laws of the time.

Extralegal is not quite the same as illegal. Illegal is against the law; extralegal means is not covered by the law.