Re-sorting lines in a form is always complex.  Perhaps suggest indenting / highlighting kit components instead of sorting?

To do this you would have to totally change the grouping on the form.  That is delete all groups.  Next you would have to group on if it is a kit component or not.  Not easy, you would have to know you Crystal forms.

Delete all groups?  I'd try adding a group for the component flag between #2&3... that way you don't have to redo the page break logic.

I completely agree though... not easy to do properly, if this simple step doesn't get the desired results.  Structural changes to forms get complicated quickly.

My colleague got this to work.

Created a formula: 

if ({SO_PickingSheetWrk.ExplodedKitItem}="N" and {SO_PickingSheetWrk.SkipPrintCompLine}="N" and {SO_PickingSheetWrk.StandardKitBill}="N") then
totext("2") + totext({SO_PickingSheetWrk.LineSeqNo}) else
totext("1") + totext({SO_PickingSheetWrk.LineSeqNo}) 

Inserted a new group and grouped by this formula.