Hi (in drawings)
1.) How to fuse balloons together like bolt-washer-nut combination NX 9 ?
2.) How to move balloon leaders for example in the center of the part without losing connection to part list ? I drag the leader to a more appropriate place but it loses the part number always when not connected to the edge.
1) Right click on a balloon and choose group horizontally|vertically. This will allow you to select other balloons to group with the chosen balloon.
2) To the best of my knowledge, NX 9 only allows you to associate balloon callouts with component edges.
To add a little more information to Cowski's solution, you can only group balloons if they are created using the Auto Balloon command: Stack a group of auto balloon callouts
It's available in NX9, though it's a little persnickety compared to NX10.