There are two reasons for doing new confessions:
* Churches have to deal with specific issues that come up.
* Churches' thinking develops over time.
I know of two examples of the first, though there may be others:
* PCUSA's Confession of 1967. This was about what I'll generally call social issues. It was explicitly said not to be a complete confession of faith.
* The Belhar Confession of 1986. It was originally adopted by the Dutch Reformed Mission Church in South Africa, but has been adopted by others as well, e.g. the RCA
The PCUSA also accepts Barmen, 1934, but I'm not sure that this is specifically a Reformed confession.
The PCUSA has also done two doctrinal confessions
* A Declaration of Faith, 1977.
A Declaration of Faith - Introduction. This was adopted by the pre-merger Southern church. It was accepted by the General Assembly of the PCUSA (i.e. the post-merger church), but wasn't given constitutional standing. It's the most complete confession I know that represents the current views of the PCUSA.
* A Brief Statement of Faith. (I've normally heard it referred to as the Brief Statement of the Reformed Faith.) 1983. This was adopted by the Presbyteries as an official confession. I would consider it a brief summary of the Declaration of Faith.
Arguably these do not contradict the historical Reformed Confessions, but I think from a practical point of view they do represent significant changes in the faith.
As for translation, there is a new translation of the Heidelberg Catechism. This is controversial in the PCUSA, because the PCUSA first started becoming concerned about the translation due to a reference to homosexuality present in the English that was not present in the original (although it's an allusion to 1 Cor 6:9). However the translation was largely done by the RCA and CRC. They had started the project before the PCUSA raised the issue of homosexuality in the translation, and had already fixed that section. While there's no doubt that interest in the PCUSA started because of the gay issue, once the question of the translation was opened, people found many issues. So we become involved in the RCA / CRC effort, though they continued to lead the effort. The new translation has been approved by 2/3 of the Presbyteries, so assuming that GA in 2014 agrees, it will become the official version of the Catechism for the PCUSA. It had previously been accepted by the RCA and CRC.