You shouldn't have to mess with adding a free feat and such. If you create the one-handed weapon as a copy of the Scarf, Bladed thing, and then in the new one-handed item, set it to 'Count As Weapon...' Scarf, Bladed - then all proficiency and feats (like the free weapon focus feat, for instance) should work with the 'new' one-handed scarf.
Of course, the better option would be to figure out where the BladeBound is getting the restrictions for possible black blades, and alter it there - so you can use the default bladed scarf item, instead of a duplicate. I do feel this is a bug and should probably be reported via the proper bug reporting. It is, at the very least, inconsistent with other options in hero lab. Slashing Grace, for instance, does recognize the Bladed Scarf in the Kapenia Dancer's hand, as a one-handed slashing weapon, and offers it as an available target for the Slashing Grace feat.