Could you help me with the following predicament? I'd like to change the permalink structure of my website from the current one
/%category%/%postname%/
to
/%category%/%post_id%/
in a way so that the old publications could still be reachable through the old links?
Thank you in advance!
First, you need to 100% sure you want to make this change to your site because it will probably have an impact on your SEO, positive or negative.
Once you change your permalinks have been changed your WordPress installation will update all the links itself, however, links in the menu or any hardcoded links you will need to change yourself.
But to answer your question, you are best using 301 Redirects allowing anybody who happens to stumble across an old link make it to the correct page / post. There is a plugin that can achieve this called Simple 301 Redirects. The authors of this plugin note:
It's especially handy when you migrate a site to WordPress and can't preserve your URL structure.
This is a fair case for 301 Redirects. However, with Search Engines this is beyond your control unfortunatly. You will need to resubmit your XML site map.