Playing an adrenaline card for a stat bonus can be done at any time. Page 5 of the rulebook even says, "You can use an adrenaline card for a stat bonus even if the bonus does not benefit you."
When playing an adrenaline card for the special ability, you must follow the rule on the card. In addition to the restriction that you can use some abilities only on your turn and some at any time, there is also the timing of the card's rule. If the card says to move guards, you must move them. If the card says to reroll dice, you can only use the card when rolling dice.
Thank you Will. In other words:
If I want to increase / decrease my fear by 2 or 3, I can do it anytime playing STAT BONUS of an adrenaline card without considering stat bonus icon.
Got it right?