A topic from AEG's L5R CCG Rules forum, copied for Oracle of the Void from a copy of the forum saved in October 2015, so pages it didn't save are missing. Players' names are left out; the rules officials are named. Rulings are as they stood on these dates; later rulings, the rulebooks and the Rules Archive may differ.
A player, 1 March 2008
Is "discarding the Imperial Favor" still a base cost of Imperial Summons (thus qualifying it for the reaction granted by Severed From the Emperor) if the player of Imperial Summons chooses to bow his stronghold?
Imperial Summons: Political Open: Bow your Stronghold or discard the Imperial Favor: Bow a target Personality.
Severed From The Emperor's granted ability: Reaction: Any number of times per turn, after an action with a base cost of discarding the Favor targets one of your cards: Lose 5 Honor. Negate the action's effects.
Martin Lund (rules official), 3 March 2008
Is "discarding the Imperial Favor" still a base cost of Imperial Summons (thus qualifying it for the reaction granted by Severed From the Emperor) if the player of Imperial Summons chooses to bow his stronghold?
Imperial Summons: Political Open: Bow your Stronghold or discard the Imperial Favor: Bow a target Personality.
Severed From The Emperor's granted ability: Reaction: Any number of times per turn, after an action with a base cost of discarding the Favor targets one of your cards: Lose 5 Honor. Negate the action's effects.
Yes. It is a base cost of the card and that doesn't change just because you have multiple costs to pay or cost options to choose from.