Is money earned from a temporary job, carried out in a legally illicit manner, Islamically permissible or forbidden?

The answer to the question depends on understanding the nature of the job and the type of legal violation. If the job itself violates a regulatory law that does not permit something forbidden, then the wage is unlawful (haram). However, if the violation is in the manner of obtaining the job (such as paying money or using a forged certificate), then if the work itself is permissible and you perform it with excellence, the wage is lawful (halal); otherwise, it is unlawful (haram).