If you don't want the line to disay you need to make the Actuals zero for future months in the YTD context.
As Ann-Grete suggests, if you have YTD consolidations, you could write a rule that makes Actuals 0 for future month YTD consols.
If you're just doing this within a PAW report using some MDX calculated member, you would do that by modifying the calculated member to return 0 when it intersects with future months.
Really depends how you've got things set up but the important thing is: TM1/PAW will display all the nonzero values it finds within the context of your view query, so to not display things you need to make it think there is nothing to display.