If you upgrade your server to version 2.5, you get Easy-RSA version 3, which has:
set-rsa-pass <filename_base> [ cmd-opts ]
set-ec-pass <filename_base> [ cmd-opts ]
to change your passwords ..
You don't even need to upgrade your Openvpn server, you can download Easy-RSA3 from here:
https://github.com/OpenVPN/easy-rsa
And if you feel really adventurous then you could even try this:
https://github.com/TinCanTech/easy-tls
Or, you can try to decipher this command:
easyrsa_openssl "$key_type" -in "$file" -out "$out_key_tmp" $crypto ${EASYRSA_PASSIN:+-passin "$EASYRSA_PASSIN"} ${EASYRSA_PASSOUT:+-passout "$EASYRSA_PASSOUT"}