After France was humiliated by Britain in the Fashoda Incident of 1898, the French wanted the alliance to become an anti-British alliance. In 1900, the alliance was amended to name Great Britain as a threat and stipulated that should Britain attack France, Russia would invade India.
Efforts so far
The original text of the Convention is available here. I've tried unsuccessfully to find an online version of the 1900 amendment. The Wikipedia footnote at the end of the containing paragraph points to Taylor's The Struggle for Mastery in Europe, which refers to it on pp.338-9, but with sources that appear to relate only to the 1892 version.
Searches on the French National Archives for "1892", "1892 convention" and "1900 convention" (all without quotation marks) and "Alliance Franco-Russe" (with quotation marks) turned up a small enough list of results to look through manually. None looked relevant.
I've included the "world-war-one" tag for this question since the Convention is relevant background to WWI.
On the advice of Mark C. Wallace I now add the comments below this question to the main text.
Although this is phrased as a source request, I believe this is within the guidelines we've developed. OP is asking (effectively) for a transcript of a primary source; that should not result in the kind of subjective disputation that surrounds other source requests. Can anyone help OP? – Mark C. Wallace
The French national archives, that store government papers, is the most likley place to look for the original amendment text. See also question: world war one - Was Wilhelm II aware of the Franco-Russian Military Convention 1892? - History Stack Exchange – Mark Johnson
@MarkJohnson Searches there for "1892", "1892 convention" and "1900 convention" (all without quotation marks) turned up a small enough list of results to look through manually. None looked relevant. I got the Wikipedia link from your helpful answer to the question you link, of which I am also the OP. – mjc
@MarkC.Wallace: Agreed from my point of view also. – Pieter Geerkens
You should add that information (including link) to your question, so that a list of what efforts is known to others. May lead to furthermsuggestions. – Mark Johnson
@MarkJohnson Thanks, done. – mjc
And what results were returned when searching the french title of the alliance convention? Good knowledge of French will be important for this search task. – Mark Johnson
@MarkJohnson I assumed any results for that would be included in the more general searches I described, since "convention" has the same spelling and meaning in French as in English. A search for "Alliance Franco-Russe" now confirms my assumption by returning one of the (unuseful) results from the previous searches. I put the description through Google Translate and followed the link to be sure. – mjc
@mjc; recommend you move all the comments into the question text; the probability of an answer is inversely proportional to the number of comments. You've already asked a tough question if it has stumped P. Geerkens, and we don't want to decrease the odds. Thanks for a tough one! – Mark C. Wallace
Russian Wikipedia has sources which might lead somewhere. For example, this article mentions what you are looking for (no original text, but it clearly refers to an existing one). Also, there's another Russian source: А.В. Игнатьев. Внешняя политика России в конце ХІХ — начале ХХ века (Россия перед вызовами новой эпохи). М. ГЕОС, 2011, — 220 с., с. 137, but I can't find this online. – Lars Bosteen
The second link (this article) of @LarsBosteen Russian Army in the Great War: Project Archive B. Meetings of the Russian and French Chiefs of General Staff quotes Journal of the 1900 Meeting, Chapter IV, §4 twice. The 3rd point of this meeting is 3) Discussion of the program of the agreement against England for action in Asia and Africa. – Mark Johnson