I am talking about Version 7
1.) As far as I know you can’t configure the behaviour of serial/parallel Processing in Designer. So you would configure this attribute after Deploying your Model to the development environment. Search for the Subscription Trigger in Developer in your BP-Package and change the field ‘Processing mode’ from concurrent to serial. This configuration could be deployed to other environments
Be carefull with generating new versions of the Model, the subscription Trigger could be overwritten
2.) you could directly change the subscription trigger via Administrator/Settings/Messaging/Broker Lokal Trigger Management/*Subscription Trigger.
Change Max Execution Threads from 10 to 1. (Restart Integration Server)
Be carefull when deploying, the subscription Trigger could be overwritten
3.) you prevent parallel processing directly in your app. e.g you could use semaphores, in webMethods you might use wmPublic/Storage Services