The upside is that the two fields I'd like to add external information to are part of the file already - the PartName and the Description field.
I don't see where I can access the files that produce the ascii file to be able to add in these two things. I've done some looking in the forums here and don't see anything that looks relevant to this.
As Pete mentioned above, there are easier pathways.
Search for Attributes.Add in the help, and there is also a ECO pathway that uses *DEL_ATTRIBUTE* and *SET_ATTRIBUTE*.
If you really want to work on the ASCII file, life is a little easier if those fields are already there.
You need to find the RefDes, then scan ahead to the AttrName match, and insert the new value, doing this for every part.
If the customer does not have PADS, and wants to control this information themselves, then the ECO pathway may be best.
You send them a BOM, and they send back a ECO ASCII file that you apply to tag new numbers. You can repeat the BOM for them to verify.