Настройка rewriterule - Joomla 2.5: Общие вопросы

Добрый день. Помогите, пожалуйста!
Итак задача. У нас есть таблица с товарами (очень большая). В силу разных причин решили сделать новую таблицу с товарами. Частично она пересекается с первой таблицей, частично нет.
Хочется мягко перейти от старой таблице к новой. На сайте хочется показывать товары из новой таблицы, на не хочется потерять трафик на проиндексированные страницы из старой таблицы.
Самый логичный способ изменить url страниц на сайте.
Если пользователь пришёл по старой ссылке, то показать ему старую страницу, если по новой, то новую
url старых страниц выглядит следующим образом:
unitnsk.ru/kupit/setevoe-oborudovanie/netifo-na-100w-32-bit-fast-ethernet-card-10-100.html

url новых страниц будет выглядеть так:
unitnsk.ru/cena/setevoe-oborudovanie/netifo-na-100w-32-bit-fast-ethernet-card-10-100.html

Напрашивается решение изменить входящий url Через Rewriterule в .htaccess

Попробовал сделать так, но он выдаёт 404 ошибку. Помогите, пожалуйста разобраться.

##
# @package Joomla
# @copyright Copyright (C) 2005 - 2012 Open Source Matters. All rights reserved.
# @license GNU General Public License version 2 or later; see LICENSE.txt
##

##
# READ THIS COMPLETELY IF YOU CHOOSE TO USE THIS FILE!
#
# The line just below this section: 'Options +FollowSymLinks' may cause problems
# with some server configurations. It is required for use of mod_rewrite, but may already
# be set by your server administrator in a way that dissallows changing it in
# your .htaccess file. If using it causes your server to error out, comment it out (add # to
# beginning of line), reload your site in your browser and test your SEF url's. If they work,
# it has been set by your server administrator and you do not need it set here.
##

## Can be commented out if causes errors, see notes above.
Options +FollowSymLinks

## Mod_rewrite in use.

RewriteEngine On

RewriteRule   ^kupit/(.*)$ cena/$1?unit_base=old [R]

## Begin - Rewrite rules to block out some common exploits.
# If you experience problems on your site block out the operations listed below
# This attempts to block the most common type of exploit `attempts` to Joomla!
#
# Block out any script trying to base64_encode data within the URL.
RewriteCond %{QUERY_STRING} base64_encode[^(]*\([^)]*\) [OR]
# Block out any script that includes a <script> tag in URL.
RewriteCond %{QUERY_STRING} (<|%3C)([^s]*s)+cript.*(>|%3E) [NC,OR]
# Block out any script trying to set a PHP GLOBALS variable via URL.
RewriteCond %{QUERY_STRING} GLOBALS(=|\[|\%[0-9A-Z]{0,2}) [OR]
# Block out any script trying to modify a _REQUEST variable via URL.
RewriteCond %{QUERY_STRING} _REQUEST(=|\[|\%[0-9A-Z]{0,2})
# Return 403 Forbidden header and show the content of the root homepage
RewriteRule .* index.php [F]
#
## End - Rewrite rules to block out some common exploits.

## Begin - Custom redirects
#
# If you need to redirect some pages, or set a canonical non-www to
# www redirect (or vice versa), place that code here. Ensure those
# redirects use the correct RewriteRule syntax and the [R=301,L] flags.
#
## End - Custom redirects

##
# Uncomment following line if your webserver's URL
# is not directly related to physical file paths.
# Update Your Joomla! Directory (just / for root).
##

# RewriteBase /

## Begin - Joomla! core SEF Section.
#
RewriteRule .* - [E=HTTP_AUTHORIZATION:%{HTTP:Authorization}]
#
# If the requested path and file is not /index.php and the request
# has not already been internally rewritten to the index.php script
RewriteCond %{REQUEST_URI} !^/index\.php
# and the request is for something within the component folder,
# or for the site root, or for an extensionless URL, or the
# requested URL ends with one of the listed extensions

RewriteCond %{REQUEST_URI} /component/|(/[^.]*|\.(php|html?|feed|pdf|vcf|raw))$ [NC]
# and the requested path and file doesn't directly match a physical file
RewriteCond %{REQUEST_FILENAME} !-f
# and the requested path and file doesn't directly match a physical folder
RewriteCond %{REQUEST_FILENAME} !-d

# internally rewrite the request to the index.php script
RewriteRule .* index.php [L]
#
## End - Joomla! core SEF Section.


#php_flag display_errors On
#показать все ошибки кроме предупреждений (Notice)
#php_value error_reporting "E_ALL & ~E_NOTICE"