Is it considered an innovation (bid'ah) to dedicate six rak'ahs from the night prayer daily to express gratitude for specific blessings and to supplicate for steadfastness upon these blessings?

A singular prayer with the intention of showing gratitude is not prescribed. However, there is no objection to performing the night vigil (Qiyam (definition) al-Layl) with the intention of showing gratitude. Gratitude, as mentioned in the verse, "Work, O family of David, in gratitude," means obedience. As for supplication during prayer, one of its appropriate times is at the end of the prayer, after sending blessings upon the Prophet, peace and blessings be upon him. Supplication is also recommended during prostration and in other prescribed instances.