You can change it manually too. Open the feed template (XML file and change ActionId with value 5).
Example.
<FeedAttribute>
<Id>2</Id>
<FeedCaption>Titolo</FeedCaption>
<FeedName>Name</FeedName>
<FieldNameCode>name</FieldNameCode>
<ConvertValues />
<Required>true</Required>
<IgnoreNullOrEmpty>false</IgnoreNullOrEmpty>
<UseCDATA>false</UseCDATA>
<ActionId>5</ActionId>
<AdvancedField>false</AdvancedField>
<RowSourceType>0</RowSourceType>
<AttributeControlType>0</AttributeControlType>
</FeedAttribute>