Is it permissible to add other adhkar (supplications/remembrances) to the morning and evening adhkar, such as the adhkar for the day and night?

If you have completed the prescribed morning and evening remembrances (adhkar), then remember Allah with any unrestricted remembrances you wish, without specifying or committing to a certain number. It is permissible to recite the prescribed nightly remembrances after Maghrib, such as the last two verses of Surah Al-Baqarah, based on the Prophet's (peace and blessings be upon him) saying: "Whoever recites the two verses from the end of Surah Al-Baqarah at night, they will suffice him." Similarly, it is permissible to recite the prescribed daily remembrances after the morning remembrances, such as saying: "Subhanallah wa bihamdihi" (Glory be to Allah and praise be to Him) one hundred times, based on the Prophet's (peace and blessings be upon him) saying: "Whoever says 'Subhanallah wa bihamdihi' a hundred times in a day, his sins will be forgiven, even if they are like the foam of the sea."