The WcfEventHandler is normally used to intercept such calls but in my testing it is not fired when a metadata file is loaded or extracted. This page has a list of the service types that can be intercepted if you want to try for yourself:
Can I execute a BR after saving data? | OneStream Community
You might be able to avoid a custom development by securing the Load/Extract function (ApplicationLoadExtractPage) and then have a Data Management sequence that has steps for load and validation. The Application Control Manager solution I think has some BRs for loading metadata.