Solved How to replace a string in a file

Hello,
I have a rejection constraint before insertion into the table T lines that come from the file.
It looks if the foreign key exists in the destination table else it rejects this line.
there is a mechanism that makes a exceptionde rejection ??
because I want to insert a line in the even if the the foreign key does not exist in the table

if such mechanism does not exist I thought about this alternative:
The input file contains lines with /t as separation
I want to edit the file to each time I encounter a string 'xxx' by 'yyy'; because xxx is not existe like foreign key the template reject him

Thank you,

Zineddine

thank you Pierre-Olivier,
I want to include just the key 'yyy' and not integrate other string that come from the file if it does not exist in the table as FK, it is an exception for that key 'yyy'.

Pierre-Olivier Mazen wrote: Then, you have another possibility: make an external join to the Parent table and, in the Mapping expression of the column use something like :
CASE
WHEN FK.COL IS NULL THEN NULL
WHEN FK.COL IS NOT NULL AND PK.COL IS NULL THEN 'yyy'
ELSE FK.COL
END