When using JSON codes to customize the list form body with one or more sections consists of some columns, JSON codes reference columns here by using their internal name.
In fact, what you pointed out in the picture below is the display name of Department column.
So, it is not possible to keep the display name of Department column and have another name in the customized list form body at the same time.
The only way to change column name in the custom list form body is to change the column display name.
1.Select the Department column -> Column settings -> Edit.
2.JSON codes.
3.Result.
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