Hi guys
I must insert in a html site a htaccess file that create a redirect 301 to
the site home page for every page that gives error 404 (Page not found), but
without affecting the single redirect 301 already present in the file
htaccess regarding other subpage moved and renamed in the past.

The purpose of all of this is not losing the google page rank that can be
passed trough every bad written back link .

What do I write in the htaccess file to do this? Do I have to write it
before or after the existing rules?

Usually I have only one or two error 404 for months to redirect: I wouldn't have to have a penalty for duplicate pages, isn't it?

Thank you

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You have never see 18th gift ideas like these? (regalos empresas on español)

doesnt matter whether you write before or after in the .htaccess file because the bot will read the complete file before assuming any action in regards to your moved pages.
hope that answers your question

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I imagined, but the problem is not losing the google pagerank.
meanwhile thanks
bye