With CL_GUI_ALV_GRID I already modified some total record value, handling event after_refresh:
Check if already processed (some attribute set)
yes, " already done
Clear attribute
Exit,
no, " we got some job to do
Call method get_subtotals,
Update the returned itabs,
Set attribute
Execute method refresh_table_display .
With this method, every customer total must be calculated from standard total, but you can also change a text, add a warning icon, etc.
Alas I never looked for an equivalent in cl_salv_table...
Regards,
Raymond