First Define Your Terms
First of all - it depends what we mean by "manipulate."
If I smile at someone when we are introduced, am I merely being polite - or am I trying to persuade them at a non-verbal level, that I'm a jolly nice chap?
For example, there are several websites that deal with the use of NLP techniques for the purposes of seduction. I guess most people would accept that as a fairly obvious form of manipulation in the sense of getting another person to do what you want them to do without them realizing what you're up to?
But wait a moment.
If this seems a little cynical, bear in mind that Professor Robert Rosenthal has demonstrated that when observers were shown three 10 second video clips of the teacher at work - but without being able to hear the actual words that he or she was speaking (only the vocal tones) - thay were able to grade that teacher's performance on several criteria to within 80% accuracy as compared with the evaluations of students who had attended that teacher's classes for several months.
In other words, just as you can use a hammer to build a shelf, or to bash someone's brains in, so NLP techniques can be used for good or ill.
Knowledge - on its own - is NOT "power"
There are certainly some fairly subtle techniques for gathering information about how someone thinks, for example - such as whether it's in sounds, feelings, pictures, etc. But that kind of information isn't much good unless you know how to use it. And once you start to use this information in a manipulative manner, you need to start thinking about another important question: "What happens when people find out what you're up to?" Because "as sure as eggs is eggs" they will realise it, consciously, sooner or later.
An excellent example is the behaviour of certain members and associates of the "New" Labour Party in the UK since they came to power in 1997.
Note: I'm not suggesting that the Labour Party have knowingly used NLP techniques as such - I have no idea whether they have or they haven't. The point is that they had certainly been attempting to manipulate the media and voter opinion in a BIG way, partly by using a number of techniques which are also part of the NLP toolbox - reframing, etc. Even with the assistance of a small army of professional manipulators, however, they were obviously unable to escape the consequences of their actions.
Postscript: In 2010 the Labour Party was led by one of the most inept communicators since Michael Foot. In the face of such an uphill struggle even the Party's most adept spin doctors could do nothing. Labour "went down in flames" (as compared to their previous results), and the erstwhile leader of the party has seemingly gone into hiding apart from a brief appearance at the funeral of the one time shop steward of the Amalgamated Union of Engineering Workers and leader of the famous Clydeside shipbuilders' "work in" of 1971.
Recommended reading: Influencing with Integrity. Most NLP books cover this question to a greater or lesser extent.