Hello aspose team!
<?xml:namespace prefix = o ns = "urn:schemas-microsoft-com:office:office" />
Thanks for your inquiry. In one of future version we will consider to provide an ability to get Field object by FieldStart. This will allow you to iterate through all Fields and update only required fields. We will let you know once this issue is resolved.
Thanks for your inquiry.
You may want to look into using the code from this thread here which may work for you in the mean time.