You certainly can by putting in a suitable expression.
I expect you will need to use the GetCurrentSelections() function, here is the url to the Help for it :
It there are no selections then it will return nothing and have a length of zero that you could use in an if statement using :
So you maybe need something like :
= if ( len(getcurrentselections()) = 0 , 'Total Revenue' , 'Partial Revenue' )