Is it permissible to deliberately invalidate one's ablution after the Asr prayer in order to occupy oneself with the two rak'ahs of wudu until the mosque opens for the Maghrib prayer, given that the mosque closes after Asr and one is forced to leave, while desiring to remain for the reward of the Maghrib prayer?

It is detestable to deliberately create a reason for prayer (like performing ablution or entering the mosque) during times when prayer is forbidden, with the intention of praying. An example would be entering the mosque not for a need but solely to pray the greeting of the mosque (tahiyyat al-masjid). This detestability is a prohibitive detestability (karahat tahrim), and what is obligatory is to occupy oneself with the remembrance of Allah Almighty, reciting the Qur'an, and similar acts. Furthermore, reward is obtained by intending to stay in the mosque, and by awaiting prayer even if at home, for the worship and remembrance of Allah are not confined to the mosque.