Check where the documents are linked

Ashwin_CH 

SharePoint will take care about it so link will be automatically updated when you rename any document. (Of course, if you have sent direct document link (Absolute URL) separately to anyone or some have bookmarked with Absolute URL then it will not work)

CSOM - PowerShell Reference -> How you can renamed document

https://morgantechspace.com/2016/09/how-to-rename-document-in-sharepoint-powershell.html#:~:text=There%20is%20no%20direct%20function,same%20location%20with%20different%20name. 

Official Documentation: https://support.microsoft.com/en-us/office/rename-a-file-folder-or-link-in-a-document-library-bc493c1a-921f-4bc1-a7f6-985ce11bb185#:~:text=Open%20the%20document%20library%20and,field%2C%20and%20then%20click%20Save. 

So I think now answer of second question is not required 🙂

Hope it will helpful to you.