When you modify cifs permission of a dataset, it wont update the existing members cifs settings.
It will be applicable to the new members that will be provisioned here after.
To give each member a different cifs permission settings, you can follow the steps like this,
a) Create a dataset without any export settings configured.
b) While provision a member in the dataet, you can give cifs permssions like this,
"dfpm dataset provision -n <name of share> -s <size> -m <cifs-domain> -p <user[:right..> <dataset>"