Bull. The RCC do not officially change scripture.
Unofficially, they don't do it either.
They change interpretation and explanation of scripture.
I believe one of their defining principles since the Age of Reason has been "Where our understanding of scripture disagrees with physical evidence, it is our understanding of scripture that is at fault." Understanding of scripture, not the scripture itself.
Hmm.. well.. do they really change the interpretation?
Could you give some examples?
I thought it's the catechism that changes, and it is based on other sources as well as bible. Different vatican congregations etc can also change the rules. the whole infallibility of the pope is often misunderstood as well, there's a number of conditions that need to be present for the papal teachings to be considered 'ex cathedra'
Source from
http://en.wikipedia.org/wiki/Papal_infallibility :
For a teaching by a pope or ecumenical council to be recognized as infallible, the teaching must make it clear that it is definitive and binding. There is not any specific phrasing required for this, but it is usually indicated by one or both of the following: (1) a verbal formula indicating that this teaching is definitive (such as "We declare, decree and define..."), or (2) an accompanying anathema stating that anyone who deliberately dissents is outside the Catholic Church. For example, in Pope Pius XII's infallible definition regarding the Assumption of the Virgin Mary, there are attached these words: "Hence if anyone, which God forbid, should dare willfully to deny or to call into doubt that which we have defined, let him know that he has fallen away completely from the divine and Catholic Faith."
Of course RCC is not the whole christianity, but the truth is, officialy, if you do not accept any of the papal 'rulings' and catechism of the RCC, you're not a part of RCC, so you shouldn't call yourself a 'roman catholic', although you can of course still remain christian. There is no single body governing the rules of christianity.
Not accepting the rulings excludes one from being a part of RCC, although if you accept them, but disobey them from time to time, you're OK, you're a sinner though and will burn in hell if you won't do something about it (confession and other methods).
EDIT:
that's interesting, from the same source, directly following the previous paragraph:
An infallible teaching by a pope or ecumenical council can contradict previous church teachings, as long as they were not themselves taught infallibly. In this case, the previous fallible teachings are immediately made void. Of course, an infallible teaching cannot contradict a previous infallible teaching.
That's the only way it can work of course, but it opens the whole infallibility to abuse, what if a pope goes mad (or becomes an extremist) and infallibly declares something he shouldn't? there's no way to reverse it.