import keypair to an existing pkcs12 keystore under a new alias name - ssl

Question

I am learning OAUTH2 and OpenID Connect and configuring multiply tomcat servers (a Client for the UI, and multiply Resource Servers for the APIs) to use SSL. So I have created a PKCS12 keystore with a self-signed certificate + private key the following way and then I pushed it under my 1st Tomcat:
(I know that the commands bellow can be simplify and combine into one (or two) but I deliberately keep tem separately because that way I can see and understand the steps better)
(1) The keypair was created with openssl this way:
openssl genrsa \
-des3 \
-passout pass:$phrase \
-out id_rsa_$domain.key $numbits
(2) Then I created a Certificate Signing Request with this command:
openssl req \
-new \
-key id_rsa_$domain.key \
-passin pass:$phrase \
-subj "$subj" \
-out $domain.csr
(3) After that I created a x509 certificate:
openssl x509 \
-req \
-days $days \
-in $domain.csr \
-signkey id_rsa_$domain.key \
-passin pass:$phrase \
-out $domain.crt
(4) Finnaly I have created a key-store in PKCS12 format:
pem=$domain.pem
cat id_rsa_$domain.key > $pem
cat $domain.crt >> $pem
openssl pkcs12 \
-export \
-in $pem \
-passin pass:$phrase \
-password pass:$keystore_pwd \
-name $domain \
-out example.com.pkcs12
rm $pem
At the end of this process I have the following files:
id_rsa_authserver.example.com.key: the private (and public) key
authserver.example.com.crt: the self signed certificate
example.com.pkcs12: the keystore
Inside the .pkcs12 file I only have one key-pair entry under the authserver.example.com alias. I have checked the result with KeyStore Explorer as well and everything looks fine and the 1st Tomcat works properly with that keystore.
Then I repeated the steps (1), (2) and (3) and I generated new files for order.example.com host machine and at the end I have two new files:
id_rsa_order.example.com.key
order.example.com.crt
Now I would like to add to my "root" example.com.pkcs12 keystore this new keypair + certificate under the order.example.com alias in order to I keep all certs that I use for my demo in one keystore. I can do it easily with the KeyStore Explorer tool via the tools > import key pair > openSSL > browse the private key and cert files, but this is not enough good for me. I would like to do the import via command line using OpenSSL.
Unfortunately I have not found the proper openssl command that I can use to ADD my 2nd key+cert to the existing keystore.
What is the command that I can use?