[user5994461]

No, they're not stable.

My current ISP in the UK and my previous one in France are changing IPs every few weeks or so in practice, or when the box is rebooted, or when the connection is lost for a while between the box and the ISP.

The game server would prevent many (most?) players by whitelisting IPs, but I bet they couldn't care less about blocking players or they wouldn't require whitelisting in the first place.