#!/bin/perl5

use strict;
use warnings;

my $tag = { K =>  { open        => '%',
                    close       => '',
                    block       => 1,
                    block_open  => '<p>',
                    block_close => '</p>'
                  },
            R =>  { open        => '<li>',
                    close       => '</li>',
                    block       => 0
                  },
            T =>  { open        => '<td>',
                    close       => '</td>',
                    block       => 0
                  }
          };

my $block_flag  = 0;
my $line_out    = '';
my $output      = '';

while (my $line_in = <DATA>) {
  chomp($line_in);
  my ( $style, $content ) = $line_in =~ /^(\w)\s+(.*)$/;
  $line_out = join( '',
                    $tag->{ $style }->{ open },
                    $content,
                    $tag->{ $style }->{ close } );
  
  if ( $tag->{ $style }->{ block } and ! $block_flag ){
    $output = join( '',
                    $output,
                    "\n",
                    $tag->{ $style }->{ block_open },
                    $line_out );
    $block_flag = $style;
  }
  elsif ( ! $tag->{ $style }->{ block } and $block_flag ){
    $output = join( '',
                    $output,
                    $tag->{ $block_flag }->{ block_close },
                    "\n",
                    $line_out,
                    "\n" );
    $block_flag = '';
  }
  else{
    $output = join( '',
                    $output,
                    $line_out );
  }
  $line_out = '';
}
open OUT, ">", "output.txt" or die;
print OUT $output;
close OUT;

__DATA__
R Whatever
K Perl
K Monks
K Is
K Cool
T Another style
R Whatever
[download]

Produces...

<li>Whatever</li>
<p>%Perl%Monks%Is%Cool</p>
<td>Another style</td>
<li>Whatever</li>
[download]

A bit extreme, not elegant. But flexible and easily changed if formats change or are added.
Hope this helps
wfsp