Vadim,
When I use the logic as stated by you :
*REC(EXPRESSION=(([G_CUSTOMER].[ALL],G_VENDOR].[ALL],[GVERSION].ACT],[AUDITTRAIL].[LN])==0 ? -%VALUE% : 0, AUDITTRAIL = REVERSAL)
It creates records with 0 and AUDITTRAIL = REVERSAL, for the condition false.
I dont see any records for budget with negative sign in Audittrail - Reversal.
Regards,
Shrini