Is it permissible to consistently observe the supererogatory acts (Sunnah), or is it permissible to sometimes omit them so they do not take on the ruling of an obligatory act (Fard)?

Preserving the regular Sunnah prayers (Sunan al-Rawatib) and supererogatory acts is commendable and recommended due to the practice of the Prophet, peace and blessings be upon him, and his saying: "The most beloved of deeds to Allah are those that are most consistent, even if they are few." So, there is no harm in observing the Sunnah prayers, but the servant must know that they are not like obligatory (fard) prayers, and he should intend them as supererogatory acts and clarify this to people. A person might encounter an occupation, travel, or illness, in which case he can leave them at that time, but he should not intentionally abandon them. Some Sunnah acts are better performed sometimes and left sometimes.