Idocs- not to overwrite client data

Hi all,

I am using CREMAS03 and I have an interesting requirement.

I am using file port, so on the load side I have a conversion program which manipulates idoc file and creates idocs from it.

The requirement is that I have to retain the basic data ie client level data ( like LFA1 , LFB1 etc) and extend views like LFM1 etc.

I tried with the MSGFN field but it didnt work.

Does anyone has any idea ?

Thanks & Regards,

Ankur