The title alone should suffice to say there will be spoilers throughout.
Let's say I give the Eyes of a Firekeeper to the Firekeeper, as well as follow Yoel and Yuria's questline as necessary. Then I kill the Soul of Cinder. At this point, standing in the empty arena, I haven't interacted with the Firekeeper's summon sign or the bonfire. Can I at this point return to Firelink Shrine and do things to alter which ending I'll receive, such as killing the Firekeeper to take back the eyes, or kill Yuria, or heal the Dark Sigil? I'm specifically asking for the sake of me being able to summon NPCs for the finale, but wanting to get the trophy for the "To Link the First Flame" ending.