I have a website with WordPress and have about 60 categories with 3 or 4 levels.
Now I want to change many category's levels and maybe some slugs. for example a category such as "wordpress" is level 0 move to level 1 by "Content Managent system" parent and so on.
Would this be bad for my SEO?
If you change the category slug or change the level or category then old URL will return 404 error and this will cause ranking drop (you might also see reported errors in Google Search Console). If you want to save the positions then you need to redirect 301 old URLs to new URLs after change.
As far as I know if the URL of category or post changes there is no guarantee that the site positions will remain the same. You can use 301 redirect to let Google know the page was moved. You can configure 301 redirects using Wordpress plugin or by configuring the web server directly.
Changing your URL structure can be dangerous but is an important step at same time Google counts on the URL to identify the site structure and semantics.
I would recommend going through the process but doing it carefully, start by mapping down your site and making changes one by one and 301 redirect the old slug/url to the new one. If you have time i would recommend conducting the changes to one category first, see the results and then move to the rest.
Things to consider: 1. 301 Have a potential link bleed of 90% to 99% 2. Use structured URL instead of flat.
Good Luck
