I have an older (1950) house and the BX cable in a heavily used light fixture box is my concern. While updating the kitchen, I plan to change the light fixture box to a junction box and add two (2) small recessed lights just below that location behind thew cornice (over the sink). The insulation flaked right off while handling the wiring to splice with wire nuts. I was able to re-tape and "managed" but was considering replacing this segment. I believe this segment comes from the main overhead light and the switch wiring comes up the wall to meet in this "subject" box. How difficult is it to replace.. in other words, can new wires be pulled into the BX jacket or does the whole segment have to be ripped out and pull in another.. possible Romex. Is there a trick to doing this ? I suspect there might be ? Thanks, Ron :D

Is there a trick?

Electrician is synonymous with magician.

No, cannot pull new wires through the sheathing. Just impossible.

Need to drill through wall and ceiling framing members. There is usually 2 2x at the top of a wall, and may have to cross several joists to get to the ceiling.

The trick is to find a path from the switch, up, over, down, how ever a cable can be run, through the least amount or most accessible holes or path.

Many times there is just no way or to make it very simple is to just break open holes at the wood locations to notch or drill through the wood to get a cable from point A to point B.

Fishing, without too many holes, or none, takes a certain touch, someone with experience.

Some pictures of the area will help.