Custom column for report using Power BI Dataset

I'm trying to create a report in Power BI Desktop using a Power BI Dataset sitting in a workspace.  I want to customise some values for a report showing animal data.  Specifically, for the column "Current Animal Type", I want to change the values "Cat" and "Kitten" to "Feline". 

Normally, I would add a custom column and use the following DAX to acheive this:

New Animal Type = IF('Animal'[Current Animal Type] IN {"Cat", "Kitten"}, "Feline", 'Animal'[Current Animal Type])

However, the ability to add a custom column to my report is disabled when using a Power BI Dataset.  Is there another way to achieve this?

Please note, I do not have the ability to change the dataset and I only want to do this for one report.  Any help you can give will be much appreciated.