For multi-leader just select another leader line without a break line. Click on the object first and then the existing leader you want to add to. Once connected you can click on the node and slide it where required, like up next to the break line on the original if you use them.
For breaks/jogs, select the leader with a left click to highlight it. Once selected, hold the ALT key down and left click again to select a point along the leader where you want to add the break. Then select the node created and drag it where required. Likewise, you can remove a leader by holding the ALT key down and selecting the node to remove it.
I was reading about your solution to adding multiple leader lines to a dimension. But I could not still add them. I use NX 10. Can you guide me using a screenshot for the command?
Thanks a lot!