Hello, I have the same problem,
RedirectMatch 301 old_url1 new_url1
Doesn't work, it do nothing because prestashop have 2 rules
RewriteRule ^.*$ - [NC,L]
RewriteRule ^.*$ %{ENV:REWRITEBASE}index.php [NC,L]
Which redirect everything to index.php and later url is rewritten by PHP.
If anyone have idea how to solve this problem please write us.