I'm looking for a way to hide one status if Service = 'x'. Does anyone have any ideas on how to achieve this?

Here is a simple solution which will work for a status...you just cant run in list type queries from here as far as I can work out.  The example below will hide the Waiting for 3rd Party status if the service desk service is selected:

Expression:

$(if [ValidationList]Service == "Service Desk"
then "Waiting for 3rd Party"
else "")