The notation use to enter relation in assembly mode are differes from the notaion use to enter in parts mode.
In assembly mode, for each assembly parameter, you must specify a "session_ID" that refers to a component in the assembly.
Session ID can be get from relation menu.
For example, parameters in an assembly appear for part with session_ID 1 as d0:1, d1:1 etc where as for part with session_ID 3, they appear as d0:3, d1:2 etc
Hope this will throw some light on your requirement.
Cheers...
Yogesh Birari