The rules for novice drivers (often somewhat misleadingly called jeunes conducteurs or "young drivers" whereas the age of the driver is irrelevant but rather the age of the driving licence matters) comes from the fact they have a permis probatoire, or probationary licence, which is in effect during the first three (or two, under conditions) years after a new driver's licence is issued to someone. Adding a category is not considered to create a new driver's licence, but simply a modification of the authorization contained in the licence. Obtaining a licence after the original licence is cancelled by authorities (due to e.g. loss of all points) however is considered as obtaining a new licence and a new probation period applies.
For holders of foreign licences
In principle, all rules for licencing provided by French (or another country's) law are only for licences issued under French (or that country's) law, unless expressly provided as applicable to licences issued to another jurisdiction. For example, if French law requires 20 hours of practical instructions to obtain a driver's licence, your German licence obtained from 12 hours of practical lessons of course is not simply invalid because of that unless French law expressly conditions its acceptance on the hours of instructions (which would violate the EU directive, but that is just an example.)
For example, before 2016, foreign drivers cannot be concerned by demerits point under the French system. In 2016, a new provision had to be created in the Highway Code to expressly provide for a point system for foreign drivers, which is still completely separate from the system for French licences.
French law currently only apply probationary period to licences issued under the French law. The probationary period is introduced by the point system under L223-1 of the Road Code.
This point system does not apply to holders of foreign licences as there exists a separate point system provided by L223-10 (although the system has not been implemented).
Thus, drivers holding a foreign licence recognized as valid under French law (e.g. all EU licences) are not subject to the rules for probationary drivers (e.g. letter A sticker or special speed limits). However, if a holder of foreign driving licence wish to obtain a French licence, the licence obtained as such will be considered as a new licence and subject to probationary period (but the period count as starting from the grant of the foreign licence in case of exchange) (the transportation department's response to a Senator's question, see also L223-11).
