Hello! If you want to change what Aeran's initial relationship is set to, you will have to back up to an earlier save and redo that option. There is no way to set it to something later. I would say this is only really important if you want optional romance content with him—he is unique in that he is the only romanceable companion where you have to flag your MC having feelings for him when he is introduced, otherwise you will be locked out of all potential romance content with him.