The Malaysians have had several missteps and issues in their investigation of the flight's disappearance. They have been attempting to dissuade other nations from assisting in the investigation as well as apparently attempting to collude evidence of any issues that may have occurred. They are not forthright in their presentation of evidence, therefore it would appear that they are trying to hide something. Whether it is incompetence or something more insidious is debatable, but they do appear to be hiding something.
With such an international cast of helpers and spectators, how could the Malaysian government possibly hope to cover anything up? With the entire world watching, and assisting in both the investigation and the search, some evidence of government conspiracy would surface. Someone in the government would leak the information for money.
We may never know what happened now to flight MH370. This is not necessarily because the Malaysian government is hiding anything about the investigation of the flight, but through their own incompetence have allowed the investigation to fall apart. This has allowed simple mistakes to snowball and form an avalanche of mistakes and misinformation and bungled search attempts.
Anything is possible, of course, but I don't think it is very likely that the Malaysian government is trying to hide something about flight MH370. It can be very hard to find plane wreckage when it goes down in the ocean. Also, people make mistakes and that is probably what this was when it comes to the words being changed.