I have a kdl-48w605b and the remote is a rm-ed059. This can actually control the tv, Sony 5.1 system and the ps4 impressively.
My question is, is it possible to programme the remote to control an external, non Sony device? In this case, either a sky hd box or a humax freesat box?
No, the Sony remote control is not programmable. It controls other devices via HDMI-CEC functions. However the Sky remote is programmable. Search google for Sky Remote codes.