Only way to update the linked subreport location is to delete the original subreport from the hard drive and then set location again. Then a UI would pop up to browse to the new subreport location.
Crystal Reports 2008 SP 7
Crystal Reports 2011 SP 7
Crystal Reports 2013 SP 2
Crystal Reports Developer for Visual Studio
This feature has now been added to the Subreport Format Editor ( Subreport Tab )
You can now Browse to the location and on existing reports it shows you the fully qualified path.
Also note this functionality has been added to the .NET SDK see Knowledge Base 1870775
Crystal Reports Developer for Visual Studio, Crystal Reports 2008, Crystal Reports 2011, Crystal Reports 2013, Subreport, subreport location, linked subreport , KBA , BI-RA-CR , Crystal Reports designer or BusinessViews Manager , Product Enhancement