I think you just need to create a calculated field to replace your measure(s). To be sure I understand you correctly, do you just want the line to disappear for values over the parameter value?
You have a parameter set up as Days to Release. So you want any records where the Days to Release value is greater than the parameter selection to be removed?
e.g., If 14 is selected, then none of the Days to Release values higher than 14 should show any data...
To do that, I created Calculation 1 and replaced the "Actual" measure on your line graph. You can make Calculation5 follow suit with the same mechanism. I've attached your workbook.
If that's not what you're asking, I'll try to help if you can clarify.
Tableau Help Version11.6.twbx.zip 150.9 KB