Sorry, you need also to regenerate the snakeoil certificate and point apache to it... od Debian:
make-ssl-cert generate-default-snakeoil(possibly you need to move from the way the old files)
It will create /etc/ssl/certs/ssl-cert-snakeoil.pem and /etc/ssl/private/ssl-cert-snakeoil.key
In apache config:
SSLCertificateFile /etc/ssl/certs/ssl-cert-snakeoil.pem
SSLCertificateKeyFile /etc/ssl/private/ssl-cert-snakeoil.key