Is this a safe way to extend this wiring?

The picture below is just above our cooker extractor hood underneath the first floor floorboards. I need to bring through the 140mm diameter ducting from the extractor hood. I need to do this in the top left of the picture next to the ceiling joist and wall due to the location of the hood. One of the The diagonal wires in the picture is completely taught and so is right in the way.

The only way I can think of to deal with this is to cut the wires, wire me end into a junction box fixed in the bottom left of the picture. Connect the other half of the wire into another junction box fixed in the bottom right and run a short length of new wire between the two junction boxes thus describing 2 sides of a square.

I’ve no complex electrical experience but this seems simple and logical to me.

Is there anything I am missing or which I need to take account of?

Thanks! 🙏