An ugly hack would be to create a measure to check if the row of the table is the TOTALS row and if it is display a text label there that could be an expression aka as dynamic. Then you can put a period or other tiny character into the label which is to be as invisible as possible. Lastly you put a space instead of the word Totals into the placeholder/label too.
This way you lose the ability to display totals but you get the ability to have dynamic labels.
The expression you can use is:
=If( IsNull(RowNo()), 'Dynamic Sales label #' & (-1+2) , Sum( Sales ) )
So if the RowNo() function returns a Null value the table is at the Totals row and you want to calculate a specific expression to display a dynamic label. If the row number is not null then it is a regular row and should calculate the normal expression.