Unless you've bought a rom pack (either starter of full) or by being gold membership (don't have it myself, so I don't know for sure).
Then you'll be able to set your own title, like I did with mine (bought the starter pack).
Lifetimers, those that bought the legacy of romulus pack, those over 1000 days gold have options to change their user title in the User CP.
Post rank (which is what ensign, lt, etc are) are yeah just done by post count and those are automatic with no way to change between them.
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I paid the 2500 zen for the starter pack so I have the survivor title. Pretty good deal considering I basically just wanted the tier 5 T'varo and for just 500 zen more I got a load of other stuff. Never the less, I don't use the forum title. I'd rather be known for being a Captain than just a survivor.
"The Galaxy Explorer would be fine if only it could execute it's saucer separation while moving."