Why did he change the ministers story? It actually went like this:
First they came for the Communists,
and I didn’t speak up,
because I wasn’t a Communist.
Then they came for the Jews,
and I didn’t speak up,
because I wasn’t a Jew.
Then they came for the Catholics,
and I didn’t speak up,
because I was a Protestant.
Then they came for me,
and by that time there was no one
left to speak up for me.
About the minister's story... See
http://www.history.ucsb.edu/faculty/marcuse/niem.htm
Excerpt:
There are in fact several "correct" versions. Niemöller named different groups when he first coined the saying, probably in 1946, than when it was revived in the 1970s and he was asked about it.
The groups he mentioned in several 1946 speeches were (in order, see below): Communists Incurably sick Jews or Jehovah's Witnesses (depending on which speech) People in occupied countries.
In 1976 Niemöller was asked about the quotation in an interview. The Martin Niemoeller Foundation in Germany takes his 1976 answer to be definitive. In his long answer Niemoeller mentioned the following groups, and that he started using the quotation only shortly before [see: ]: Communists Trade Unions Social Democrats Jews (sort of).
I don't think that 1976 statement reflects what Niemöller had said years earlier. The first documented reference to the precise quotation that I know of is in the 1968 Congressional Record (see below). It was certainly varied by the person testifying (Howard Samuels), who referred to Niemöller as the originator. That person listed: Jews Catholics Industrialists/Trade Unions Protestant Church.
I think the 1968 citation ONLY proves that the quotation was said much before 1976, but not which groups Niemöller actually said. Niemöller would not have said the groups in that order, and he wouldn't have named the Catholics at all, in my opinion (as well as other scholars').