You can still bind normal event handlers as well. Just update whatever variables you need, then call the updateGraph() function manually.

Something like:

my $viewbutton = $mw->Button(-text=>"Change view", -command=>\&changeV
+iew);

...

sub changeView {
    $viewmode++;
    if($viewmode > 3) {
        $viewmode = 0;
    }
    updateGraph();
    return;
}
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Tk::Chart is an extension of Tk::Canvas, which has support for Mouse interactions. You probably want to use $canvas->bind() or something similar to get mouse interactions with the canvas as event callbacks. To quote the documentation:

The only events for which bindings may be specified are those related 
+to the mouse and keyboard (such as Enter, Leave, 
ButtonPress, Motion, and KeyPress) or virtual events. The handling of 
+events in canvases uses the current item defined
 in "ITEM IDS AND TAGS" above. Enter and Leave events trigger for an i
+tem when it becomes the current item or ceases to
 be the current item; note that these events are different than Enter 
+and Leave events for windows. Mouse-related 
events are directed to the current item, if any. Keyboard-related even
+ts are directed to the focus item, if any (see 
the focus method below for more on this). If a virtual event is used i
+n a binding, that binding can trigger only if 
the virtual event is defined by an underlying mouse-related or keyboar
+d-related event.
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Frankly, i would have to spend a few hours of reading and testing on how exactly this would all work related to your graphs (which i leave as an excersise for the reader), but it sounds promising for what you want it to do.