I think you can do something like this (untested), where you have the callback just be a wrapper that passed an extra param to say where it came from:

   my($entry_Limit) = $root->Entry (
      -justify => 'left',
      -textvariable => \$Limit,
      -validate => 'focusout',
      -validatecommand => sub { Validate_Number 'entry_Limit', @_ },
   );

sub Validate_Number ($$$$$)
{
   my $caller = shift;
   my $NewValue     = shift;
   ...
}
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