you can profit the <<Modified>> virtual event (see it here), for a first-time-only modification, like in,

use strict;
use warnings;
use Tk;

my $mw = new MainWindow;

my $text = $mw->Text(qw/-width 40 -height 10/)->pack;
my $current_color = "black";
$text->configure(-insertbackground => $current_color);
$text->configure(-cursor => "arrow");
my $button = $mw->Button(-text => "Quit", -command => sub { exit })->p
+ack;
$text->bind('<<Modified>>', sub{warn "text changed\n"} );
MainLoop;
[download]

And you c an also play resetting $text->editModified to zero but follow what our wise zentara said about avoinding an infinite loop: Re: Using Tk::Text and '<<Modified>>'

See also Onchange-like event handler for Tk text widget

L*

PS you can have a better control, but still not optimale with:

my $len;

..

$text->bind('<<Modified>>', sub{
                                if ($len != length $text->Contents ){
                                    $len = length $text->Contents;
                                    warn "text changed ($len)\n";
                                    $text->editModified(0)
                                }
                             }
);
[download]

or better (but breaks on backspaces..)

$text->bind('<<Modified>>', sub{
                                if ($len ne $text->Contents ){
                                    $len =  $text->Contents;
                                    warn "text changed\n";
                                    $text->editModified(0)
                                }
                             }
);
[download]