At least I get a mouse cursor of an hourglass via
-cursor => 'watch'
building on your suggestion. Interestingly, I lose the
-relief => 'sunken'
effect unless I include this specifically within the "Busy" call. Trying to sneak in other options such as 'text', 'background', and 'foreground' seems to have no effect, thus these options are commented out in my snippet.

Thanks,
Brig

my $Customized_Command_b;
$Customized_Command_b = $tl->Button(
    -textvariable => \$Custom_Command_label, # previously defined
    -underline => 0,
    -borderwidth => $bd_width,
    -command => sub {
        
        $Customized_Command_b->Busy(
            '-recurse' => 1,
            -cursor => 'watch',
            #-text => 'Processing...',
            -relief => 'sunken',
            #-background => 'blue',
            #-foreground => 'blue',
                );

        system $custom_command, @arguments, $formdir, $dir
            and warn "'Custom Command' problem: ", $? >> 8, "\n"
            and $ccmd_rc = 1
            ;

        if ($ccmd_rc) {
            $View_Custom_Log_cb->configure(
                        -background => "red1",    
                        -activebackground => "red1",
                             );
        }

        $Customized_Command_b->Unbusy( '-recurse' => 1 );
        $tl->raise();
        },
    )->grid(
        -column => 5,
        -row => 14,
        -columnspan => 6,
        -sticky => 'nsew',
            );
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