Re: use .bit and don't install official client
It's unclear to me exactly what you're asking... possibly a language barrier?
If you're asking whether you can use the .bit TLD without Namecoin software installed, the answer is no. Just like in the 90's you couldn't use SSL without installing a browser that supported SSL.
It's not necessarily required to use a full-node client (such as Namecoin Core); there's a BitcoinJ-based client in beta that is significantly lighter.
There are some sketchy DNS relay services out there that offer a centralized TLD with the name ".bit" that they claim is periodically mirrored from the actual .bit. They are not actually .bit; by definition, .bit is a decentralized system. Similarly, there are some sketchy DNS registrar services out there that will buy a .bit domain for you. However, you do not own the domain, the service does, and there have been several cases where such services vanished, taking the domains they bought with them.
Jeremy Rand, Lead Namecoin Application Engineer
: Dynamic DNS update client for .bit domains.
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