Copy Net class from Physical to Electrical

Hmmm....they really aren't related in that sense.  What are you trying to *really* accomplish?  There might be an easy solution...

I  Have DDR ADDRESS , DATA  and CONTROL . They are matched lengths and require specific spacing requirements and trace widths. Since the classes are needed in physical and electrical with the same nets I do not want to have to re-enter them in both tabs. 

Address and control will go into electrical constraints for length or relative propagation calc.  Physical class will have single ended trace widths.  Spacing class will have the spacing rules.

For diff pairs, what gets tricky is trying to put diff pair rules in both electrical and physical.  That is not needed.  IIRC, physical will override the electrical constraints on diff pair.  You can choose to either put the diff pair rules in electrical or in physical.  I generally just have the diff pairs in electrical and nothing in physical.

On lesser systems, you can create a netclass once that has both physical and spacing (I.E. for 3W rule).  

In Allegro, you create them "twice".

The software will create the class in both physical and spacing when you enter it into CM. There is a checkbox if you do not want to create it in both.