How to use Filter Change Handler to work with Page option in Graph Builder?

[#1]

Attached is an example data table. The script below tries to plot each parameter selected via the Local Data Filter in a new "Page" in Graph Builder. As it stands, the y-axis title is shown as "Median" every time a new "Parameter" is selected via the Local Data Filter.

I would like the Parameter name to be the y-axis title when new a parameter gets selected and plotted on a new "Page".

I tried using the filter change handler for this, but my script does not quite work. I think I need the index i below to be updated each time a new parameter is selected or may be there is another way. Any direction will be useful. 

XPath( "//TextEditBox" ))[i]

here is my script

Names Default To Here (1);
Clear Log ();
gb = Graph Builder(
	Size( 531, 325 ),
	Show Control Panel( 0 ),
	Variables( X( :PartID ), Y( :Median ), Page( :Parameter ), Color( :TestStage ) ),
	Elements( Points( X, Y, Legend( 34 ) ) ),
	Local Data Filter(
		Conditional,
		Add Filter(
			columns( :TestStage, :Parameter ),
			Where( :TestStage == {"A", "B"} ),
			Where( :Parameter == {"BKDVoltage", "Capacitance"} )
		)
	),
	SendToReport( Dispatch( {}, "graph title", TextEditBox, {Set Text( "myTitleGoesHere" )} ) )
);

ldf = Current Report()["Local Data Filter"] << get scriptable object;

changeTitle = Function( {this},
	print(this);
  	ldfText = Regex(ldf << get where clause(),"\(?\s*(:Parameter == .*?)\)","\1");
	if(ismissing(ldfText),ldfText = " Selected Test Parameter ");
	(Report( gb ) << XPath( "//TextEditBox" ))[6] << Set Text(ldfText);
);

fsh = ldf << Make Filter Change Handler(changeTitle());

[#2]

@jthi Thanks. Upon initial checking, your first script works as expected (even with all unchecked). It gives expected y-axis title in all cases. Second script does not show the correct y-axis title in any case (always shows Median as the y-axis title).

I will spend some more time with the two scripts and come back if I have questions.