It's not. You still have to have the complete text of the law and manually add the changes that are described in the Bundesanzeiger. It states for example something like "Change in BGB: Paragraph 123, section 45, change the word 'and' to 'and/or'. Only completely new texts would be printed in full.

The Bundesanzeiger is merely the last step in the law making process. First, the two law making institutions (Bundestag, Bundesrat) have to vote in favor of the law and the president has put his X under it. Only after the law is published in the Bundesanzeiger it takes effect.