Urgent Problem With WordPress Permalinks.

Hello everyone,

I am running into an issue with our site and am hitting a brick wall with this. Any advice or assistance is greatly appreciated.

I am in the process of doing a site redesign with different CATEGORIES from the previous site. However for SEO purposes I have to maintain the exact same links as the old site with old structure.

The way I have the permalinks structured is as follows:

/%category%/%postname%/

When I go into the individual post from the admin dashboard, I do have the option to change the URL but only the last part that includes /postname but I am unable to modify the categories.

On the old site some of the URL links were:
http://www.oldsite.com/category/sub-category/sub-category/postname

However, even if I enter a category with sub categories, only the main category appears in the link making it impossible for me to change the URLs on the new site to coordinate with those of the old.

Another thing I noticed is that as long as the postname is correct, WordPress would automatically direct to the proper page (being independent of categories. For example:

http://www.mysite.com/fictionalword/postname

If I type in the URL with a fictional work unrelated to any categories it would still direct to the proper page as long as the post-name is correct.

I would greatly appreciate some help with this!

My question:

1. Is there any way to create a custom URL following the main domain, perhaps using a plugin?

2. Is there any way to have the subcategories listed.