Is it possible to show the selected all text instead of showing all values from a parameter?

Yes. In Bold Reports^®, you can show the Selected All text instead of all values when you choose the select all option in a parameter, by using an expression. Use the following expression.

 =iif(Parameters!<ParameterName>.Count == Count(Fields!<FieldName>.Value,"<DatasetName>"), "Selected All",Join(Parameters!<ParameterName>.value,","))