Is it possible to receive a presidential pardon before being charged (a "blanket" pardon or "pass")?
Yes, here is an example. Gerald Ford pardoned Richard Nixon:
Now, THEREFORE, I, GERALD R. FORD, President of the United States, pursuant to the pardon power conferred upon me by Article II, Section 2, of the Constitution, have granted and by these presents do grant a full, free, and absolute pardon unto Richard Nixon for all offenses against the United States which he, Richard Nixon, has committed or may have committed or taken part in during the period from January 20, 1969 through August 9,1974.
But he was not charged with anything.