How to fix category url 404’s after category permalink change

I am working on SEO for a website. So, I wanted to append "-coupon-codes" to all category URLs.

My Category Base Slug is : stores

Example what I wanted to achieve redirection :

/stores/walmart to /stores/walmart-coupon-codes 

as stores/walmart is indexed in google, I want to 301 redirect to new url

I tried this htaccess :

RewriteRule ^stores/(.*)/$   /stores/$  1-coupon-codes [R=301,NC,L] 

This was redirecting all store links to /stores-coupon-code but its 404 as original category URL doesn’t contain -coupon-codes,

and if I change any permalink to include -coupon-codes, Then, the original store URL becomes 404, and redirection isn’t working.