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Last Tested: Sep 23, 2019
No - fields can be explicitly excluded at the explore level, but not the join level. You can thus exclude fields from a given join at the explore level by appropriately scoping the field name with the join name.
At the join level, fields can only be explicitly included. If fields are specified in the
fields parameter at the join level, each field not specified will be excluded.
More information in this doc.