I am usually pretty good at spotting constitutional amendments in semi-presidential countries. However, this one completely passed me by.
There was a constitutional law in Mauritania in March 2012. The text of the law is available in French here.
The reforms are quite disparate. However, one affects executive/legislative relations. The new version of Art. 42 states that a new government has to present its programme to the National Assembly within a month. There is then a vote on the programme and if it is rejected then the government has to resign.
The other reforms are significant in a Mauritanian context, notably the recognition of the multi-ethnic nature of the country.
One other reform is worth noting. There is now a clause that forbids coups. Now, I may be cynical, but I am somewhat sceptical that future coup plotters will be dissuaded from acting on their plans because the constitution forbids them from doing so. (And I’ll refrain from mentioning the fact that President Abdel Aziz came to power by virtue of a coup. Oops).