I have a question about leaving live wires inside walls
how can it be done safely?

we have an old house with lathe and plaster walls. it has rather old wires.
on the second floor (it's a duplex) we just installed a new panel and new
wiring everywhere because we broke the walls to add insulation.

we will have to break the walls in some of the rooms in the first floor
appartment too because there's no insulation in them. at the same time I'd
like to change some wires.

the problem is that these wires are common with the basement, which is
already finished. the wires most likely come from the basement (from the
floor of the room not the ceiling). the same wires split and go to many
rooms. in other words I'd be cutting some wires to add new ones, but I can't
cut power to the old wires without destroying the whole basement.

what do I need to do to make it safe to leave a live, cut-off wire inside
the wall?

I was thinking I can wrap the end in tape and put it inside a junction box
and put a cover on the box. is that OK? is there any other solution?