I got response from GTAC .
It turns out that this is now a documented process in NX ( Which i think that the "old process" wasn't)
The difference is that one has to KEEP the hidden lines setting = DASHED( RMB- View- Style)
AND turn on "Show Referenced Edges Only". ( Same dialog.)
The new procedure :
1) place the view , set all hidden edges set to Dotted.
( and maybe the color that you want the dashed edges to have)
2) Do the View dependent edit , edit the edges to Dashed font.
( now you can see the difference between the manually edited and the non-edited in the dotted /dashed.)
3)RMB the view - Settings - hidden lines : turn on "Show referenced Edges Only"
The manually edited stays dashed whilst all other disappears.
Do NOT set the hidden edges = invisible after the above, it will erase the view dependent edit....
I am not sure that this is a better process than the old. But it is covered in the manual.
Regards,
Tomas