This only makes sense when all of these have the same settings and you must not 
manually adopt them later. Otherwise copying a client resource while 
  - changing name 
  - deleting clientid & alias
   and others
is in my eyes a more convenient method.

But of course you can create an input file for nsradmin which does this. There 
is only one core line which you must repeat for each client:

  create type: nsr client; name: client_name [; other_parameters]

Finally import the file running: nsradmin -i filename

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