I’ve written a blog post for work about how much you can and can’t mess around with urls in WordPress before old links stop working. It boils down to 5 rules:
- Editing Post slugs doesn’t break old links
- Editing Post url structure (the permalinks) doesn’t break old links
- Changing both the permalink structure and the slug will break old links
- Editing the parent/child relationships of pages doesn’t break old links
- Editing the slugs of pages will break old links
For more details read the full post on the dxw blog: Keeping traffic flowing to your WordPress site after a big restructuring