VERIFIED SOLUTION i

How to change the length of an existing data field in DOC1 Designer V5 and EngageOne Designer V6

This can be achieved using two mechanisms.

1. You can delete the existing field formatting. This is achieved by selecting the field, and hitting the "delete" button, or right mouse click "remove field". This removes the existing formatting, and you can then redefine all fields at the length required, and it's a good idea to import some data with the fields at the desired length to make definition easier. Once you do this, you will need to save and issue the data format. This is how it will look in the Data Format Editor once you've deleted the field definition:
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2. Alternatively, you can export the existing data format schema, amend it, and then reimport.  Import\export of the data format schema is handled by the following:
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Blue square is the export button, red square is the import button

When you export the schema, it creates an XML type document that contains all the information about the records and fields.  We are going to change the length of the Customer Name field, and here is how it looked originally:
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Where you can see that it had an original length of 31 bytes.
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I changed this to be 50 bytes:
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After making this change, I had to change the offset value for every subsequent field by the number of bytes I had increased the Customer Name field, in this case 19 bytes.

So, when I imported the amended data format schema, and the new sample data, the field length for my changed field is correct, and all subsequent fields are correct:
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Once you are happy with the format, then save and issue the data format, there is no need to amend the data map and dictionary (unless you are changing the name of the fields, or adding a new field).
Environment Details
Product Feature: Installation / Upgrade
UPDATED:  November 8, 2017