Credo di aver risolto.

In sintesi:

Struts.xml
codice:
...
<interceptor name="check" class="it.mypackage.CheckInterceptor"></interceptor>
...

<action name="myAction" class="it.mypackage.ShowListAction">
    <interceptor-ref name="check" />
    <result name="success">....</result>
</action>

<action name="actionToCall" class="it.mypackage.MySecondAction">
    <result name="success">....</result>
</action>

<global-results>
 ...
     <result name="intTest" type="redirectAction">
        <param name="actionName">actionToCall</param>
     </result>
...
</global-results>
CheckInterceptor.java
codice:
public class CheckInterceptor implements Interceptor {
        
    @Override
    public void destroy() {
    }

    @Override
    public void init() {
    }

    @Override
    public String intercept(ActionInvocation invocation) throws Exception {
        try {

            // se testToVerify == true -> viene invocata la action "actionToCall"
            if (testToVerify){
                return "intTest"; 
            } 
            
            // else 
            return invocation.invoke();
        } catch (Exception e) {
            logger.error("Error", e);
            throw e;
        }
    }
}