I looked for official information about this from a French government source, but did not find anything. I may not have identified the correct agency, but there was nothing obvious on the web sites of the Interior and Foreign Affairs ministries, nor on that of the Douane.
According to the UK official foreign travel advice (emphasis added):
On Friday 13 November, a number of terrorist incidents took place in Paris resulting in widespread casualties. British nationals are advised to exercise caution in public places and follow the advice of the local authorities. French authorities have heightened security measures due to a risk of further attacks. The advice of the Paris Police is currently to keep movement around town to a minimum. Systematic border control checks have been implemented at all entry points into France. A national state of emergency and a three-day period of mourning have been declared (14-16 November). Public gatherings, the flying of drones and use of fireworks in the Ile de France region (Paris and surrounding area) have been prohibited.
This should mean that you are legally free to travel in and around Paris and within France as usual, although you are advised to do so only when necessary. It should also mean that you, like everybody else, are guaranteed to be subjected to scrutiny at the border when you enter (and probably also when you leave) France. (Normally, if you are travelling across a land border, you have only a chance of being asked for your papers in a random check.) I guess that your experience with the border guard should be similar whether you are entering by an air or sea port or crossing the border on land, though if they decide to check you out more thoroughly when you're traveling by train, they might have to take you off the train so they can get to their data systems.
It would be nice to know from someone who has done it whether any of this is true.
Note that there is no mention of changing the entry requirements. Holders of Schengen visas, residence permits, etc., are therefore not being categorically excluded from the country. I have read news reports of "closed borders," just as there were reports of "closed borders" in Germany and Austria a few months ago. This is just incorrect terminology that news media are using to describe the situation. In the case of Germany and Austria, I also remember reading about "suspending the Schengen agreement" which is similarly inaccurate, because the temporary reimposition of systematic border checks is in fact something the agreement explicitly provides for. (An article describing this in French can be found at www.lemonde.fr.)
As a practical matter, however, assuming your profile name and picture reflect your real name and appearance, there is probably a greater chance that you would be subjected to unreasonable scrutiny, or, worse, that you might unreasonably be refused entry or otherwise detained at the border. I do not know the French border services well enough to predict how they will behave in the current environment. If I were you, I would try to find actual stories of young Muslims who have crossed the border, to find out how it has gone for them.
My worries in this matter are largely informed by stories I've heard from mostly South Asian friends who lived in the US immediately after the 2001 terrorist attacks, and by my own observations of airport security as I flew between Europe and the US several times a year in the years since 2001. I did not travel much in France in the immediate aftermath, so I can't say whether the blatant profiling I saw occasionally in other European countries also happened there in those days, and I certainly cannot say whether it would happen there now.
Of course, if you're singled out for closer scrutiny because of your appearance, it could be as minor as an extra question or two, or a slightly longer wait during extra database checking, or it could be more significant.
If anyone has personal experience of these newly-implemented systematic border checks, it will be most helpful to let us know about your experiences in a comment or an answer.