Is it permissible to confine oneself to the Abrahamic prayer (Salat al-Ibrahimiyya) outside of Salah, knowing that Allah commanded both prayer and submission together in Surat al-Ahzab, when He said: "Send blessings upon him and salute him with a becoming salutation"?

Sending blessings upon the Prophet outside of prayer is a broad matter and permissible with various formulations. It is preferable to offer blessings before peace. The best and most complete formulation is to combine blessings and peace upon him in any wording, thereby fulfilling the Quranic command.