If you finding a way to add any text beginning of any field or end of the field in mapping section. You can use the way below:-

1. You just need to add the text in the mapping section together with the column field name.

2. Before you add the text in the mapping section, you must ensure that the toggle show as tag at the top of the mapping is disable

For example, 

Value in feed fileField MappingResult
Column name - description
Value - Length 23cm
Description: {{description}}
Description: Length 23cm
Column name - SKU
Value - ABC1234
Vendor: {{sku}}
Vendor: ABC124
Column name - title
Value - Green Leather Bag

{{title}} designed in CaliforniaGreen Leather Bag designed in California

3. There are few fields not supported to do this which are price, compare at price, image, sales price, quantity, harmonized system code and sku fields.

4. The rest of the field that not mentioned above its able to add the text beginning of the column value or end of the value.