you can add more masternodes to your cold wallet. not your vps. you do need a new ip. you maybe can add ips to your vps and reroute everything with iptables.
but i dont yet know how to do it. you could add another coin to your first vps to maximise its gain. if you want to setup masternodes for the same coin you do have to get another 1000 coins and a new vps.
I sought before an another option and i find this :
http://www.explorerz.top/das-masternode-guide.html (at the end)
#### 2 Masternodes on one VPS ####
Follow the above guide again. You don't need to install dependencies again and you don't need to compile. However, you need a new Acc 0 address and a new Masternode key. Can get them by using a separate data dir. In order to get one do:
....