Abductive Logic Programming is a computationally founded representation of abductive reasoning. In most ALP frameworks, integrity constraints express domainspecific logical relationships that abductive answers are required to satisfy. Integrity constraints are usually known a priori. However, in some applications (such as interactive abductive logic programming, multi-agent interactions, contracting) it makes sense to relax this assumption, in order to let the abductive reasoning start with incomplete knowledge of integrity constraints, and to continue without restarting when new integrity constraints become known. In this paper, we propose a declarative semantics for abductive logic programming with addition of integrity constraints during the abductive reasoning process, an operational instantiation (with formal termination, soundness and completeness properties) and an implementation of such a framework based on the SCIFF language and proof procedure.