JavaCard OS

I am writing an applet for doing some crypto-operations. How can I also put a pkcs#11-cert on the card?
I want to establish a connection to an openssl-vpn. For this I need to put the client-cert on the card, so the vpn client can get it from there. But I can only find information using opensc. If I use opensc-tools to upload the cert, is there the danger to overwrite my javacard-app? Are there other problems?

You can find some information on using smartcards as cert-storage for openvpn.
In my opinion, you don't have to format your card, because the java card should be able to emulate this.