That does more to reassure Cole than he knows. He remains Cole. And if Solas thinks he does, then that's a sign that Cole actually does. Cole idly rubs one of his ears as he nods.

"Tell me if I change. I'll tell you if you do."

Because if the magic can change his appearance, then who's to say it can't change his self? Cole doesn't know, but better safe than sorry. Solas knew the old him and Cole knew the old Solas (or, at least, so he thinks)