Given the inherent autonomy, heterogeneity, and continuous evolution of Web services, mismatches usually exist between serviceprotocols and mediatedinteractions are a common style of serviceinteractions. Given a requestor service and an interaction to be conducted, if the provider service is found unavailable, we need to identify the most suitable provider service from a set of functionally equivalent candidates to replace the original one. Current techniques analyzing protocolreplaceability can compute a replacement degree that specifies how replaceable two protocols are, but they cannot determine whether or not, and under which conditions, the effects prescribed by the requestor can be achieved. To address this challenge we propose a technique called replaceability assessment in this paper where, according to the adaptation mechanisms of a certain adapter, this technique (i) provides a set of condition pairs that determine when one protocol can be replaced by another, and (ii) computes a replacement degree. The set of condition pairs and the replacement degree are two complementary criteria to be used by the requestor for identifying the most suitable provider service.