Is it permissible for the fiancé, after the marriage contract and before consummation, to ask his fiancée for certain liberties without her family's knowledge, on the pretext that she is his wife?

Marriage has pillars and conditions without which it is invalid. If the matter did not exceed merely writing a contract to facilitate a transaction, then you are not considered this man's wife according to the majority of jurists, such as the Malikis, Shafi'is, and Hanbalis, as they hold that marriage is not concluded through writing. However, the Hanafis believe that marriage is concluded through writing.

Therefore, if it was only a written agreement, you are engaged and are a non-mahram to your fiancé, and caution must be exercised regarding seclusion (khalwa) and interaction. However, if a valid Islamic contract has been concluded for you, then you are his wife, and whatever is permissible for a husband from his wife becomes permissible for him from you, while taking into account custom for delaying consummation.

The wife has the right to refuse herself to her husband until he pays her the immediately due mahr (dower), and the wife is not obliged to obey her husband before consummation; rather, her obedience is to her guardian.