The earlier classification of fard, wajib, and other rulings concerns the binding status and proof of duties. The question of azimah and rukhsah is different: if an original ruling is established, can an exceptional circumstance ease its practical application for the affected person?
Keep two questions separate:
1. What is the original legal ruling?
2. What changes for this particular person after a recognized excuse arises?
Personal convenience cannot by itself rewrite a ruling. A valid concession requires a legal basis, and its scope must not be extended beyond what that basis permits.