I created a test report  aggregate-space-summary1 ,
How to change default  sort order ? ,
C:\>dfm report  view aggregate-space-summary help
Aggregate Space Summary Report  (aggregate-space-summary)
Shows the summary of space allocated to the  aggregates.
Columns:
          objId                Object ID
         objName               Aggregate
         parentObjFullName    Storage System
          dfKBytesTotal        Total
         dfKBytesUsed         Used
          dfKBytesPercent      Used (%)
         dfKBytesTotalCommitted  Committed
         dfKBytesCommittedPercent Committed (%)
          aggrGrowthPercentage Daily Growth Rate (%)
         aggrdfDaysToFull     Days  To Full
Default sort order is  -dfKBytesCommittedPercent.
Created Custom Report aggregate-space-summary1 
C:\>dfm report  view aggregate-space-summary1 help
aggregate-space-summary1 Report  (aggregate-space-summary1)
Catalog Name:  Aggregate
Catalog  Field                                 Field Name
             Format
---------------------------------------------  ----------------------------------
-----------  ---------
Aggregate.Name                                Aggregate  Name
Aggregate.Filer                                Aggregate Storage System (A)
Aggregate.TotalSpace                           Aggregate Total Space
             Auto-Scaled
Aggregate.Used                                Aggregate Used  Capacity
             Auto-Scaled
Aggregate.UsedPct                             Aggregate Used  Capacity %
            0
Aggregate.BytesCommitted                       Aggregate Bytes Committed
             Auto-Scaled
Aggregate.BytesCommittedPct                   Aggregate Bytes  Committed %
            0
Aggregate.DailyGrowthPct                       Aggregate Daily Growth (%)
             0
Aggregate.DaysToFull                          Aggregate Days to  Full
Default sort  order is Aggregate.Name.