i'm still not sure what exactly you are trying to accomplish. if you are just downloading tables from source to destination, and need to replace type with documentno if type="credit", you could use sql statement in datasource, something like

SELECT COMPANY

,[LINENO]

,DOCUMENTNO

,SELLTOCUSTOMERNO

,CASE

WHEN TYPE = 'credit' THEN DOCUMENTNO

ELSE TYPE

END AS TYPE

,NO

,QUANTITY

,AMOUNT

,POSTINGDATE

FROM

DBO.SOURCE

If you are just trying to update destination table with source data, you could use sql statement in source again, select primary key and document no

SELECT [lineno], documentno, type

FROM source

WHERE (type = 'credit')

(I assume that lineno is your primary key, and then use ole-db command to update the table with

update destination set documenttype=? where [lineno]=?