Existing Animation/bone editing

Hi guys,

I have the following issue: I added a sword to my character’s hand by creating a socket, made him actually hold the sword, works fine in-game.
But when I try to edit his arm positioning it always get cancelled, like I never edited his arm. Even if I recreate a blendspace.
So it seems to work only in preview.

Do I have to re-export an edited .fbx for that ?

PS: In persona, with preview disabled, I noticed the “Bone manipulation is disabled in this mode”
what is this “mode” and how to edit that ?