Is it permissible to retract a vow not to wear trousers—which I have adhered to for four years—and to wear them again with long shirts, especially since the nature of my work requires it?

Wearing trousers is either permissible or forbidden. If it is forbidden—because the mentioned conditions are not met—then fulfilling the vow is obligatory because it is a vow of obedience. However, if it is permissible—i.e., according to the mentioned conditions—then it is a permissible vow, and the person who made the vow has the choice between fulfilling it and abandoning it. The more cautious approach is to offer expiation, which is the expiation for an oath.

The conditions for a woman to permissibly wear trousers are: that it be worn under loose, concealing clothing, that it not resemble men's trousers, and that its purpose is not to imitate what disbelieving women wear.