Under no circumstances shall the Building and Zoning Appeals Board grant an appeal or variance to allow a use not permissible under the terms of this Part in the district involved or any use expressly or by implication prohibited by the terms of this Part in such district. In granting any appeal or variance, the Board may prescribe appropriate conditions and safeguards in conformity with this Part. Violation of the conditions and safeguards, when made a part of the terms under which the appeal or variance is granted, shall be deemed a violation of this Part.