CustomHeadersMap - change only one col, leave others?

If I have a POCO with a couple dozen properties, and I want to change the column header of only one of those, is there a way to declare CustomHeadersMap that contains only the property I wish to change, and leave the others intact? The statement below leaves with with only a single column when I serialize to CSV.

ServiceStack.Text.CsvConfig<TMExportFile>.CustomHeadersMap =
                new Dictionary<string, string>
                    {"MaleFemale", "Male/Female"}

The CustomHeadersMap is for taking over which headers you want serialized, so it needs to be populated with all the properties you want serialized, you can use GetSerializableProperties() to get a types serializable properties, e.g:

var map = CsvConfig<TMExportFile>.CustomHeadersMap = new Dictionary<string,string>();
typeof(TMExportFile).GetSerializableProperties().Each(x => map[x.Name] = x.Name);
map[nameof(TMExportFile.MaleFemale)] = "Male/Female";