1.
Conceptual AA, or AA understood as an attribute of a site
is affected when concrete AA is added or removed.
Site without concrete AA still has conceptual AA. Its value is "None" and may be affected, e.g. conceptual AA of such
may be affected by Fell Winter, or by Whole Villages Roused.
CRF Entry I have quoted says about concrete AA, not about conceptual AA. Conceptual AA can never be removed and adding new concrete AA, or removing existing concrete AA only affects a conceptual AA.
2.
Playing of Forewarned is Forewarned is not a company's activity. Even if a company cannot take any activity before entering a site, player is not so restricted.
Forewarned is Forewarned affects conceptual AA of site with multiple AAs by reducing a numer of concrete AAs that such site has (be removing all but one of them).
The effect of the card does not address any concrete AA to be removed. It address a site. As such it does not affect the minion sites, because Forewarned is Forewarned is a hero resource event.