Change category id ??

I know it should be in a logically named table in phpmyadmin but is there only one table i'll need to change the id in or are there more than one?

If you change the id of a product category in the hikashop_category table, you will also have to change it in the hikashop_product_category table.
If if you have categories restrictions in fields or discounts/coupons you will also have to change the id in the corresponding tables.
Aslo, if you selected a category in your modules/menus, you will have to edit them and reselect the category again via the interface.