In earlier versions, up to 5.32, COM support was a separate component, ran out-of-process from the application (“Local Server”), we had the Options utility, and the global parameters could have been set only using that utility but not from the code. The changes made using the Options utility affected all applications written with QuickOPC, because they were stored in a single place in the registry.
In version 5.33 (
kb.opclabs.com/What%E2%80%99s_New_in_QuickOPC_5.33 ) and later, COM API is built on top of the .NET components. It runs in-process with the application. There is no Options utility, but the global parameters can be changed from the code. Such changes always affect ONLY the application that changes them (in fact, only that process run – they are not stored anywhere beside memory of the process, so they need to be set each time it runs).
In .NET, global parameters are usually set using the static (C#)/shared (VB.NET) properties on EasyXXClient objects. There are no such properties in COM, but we have made COM objects that allow the developer to access these global properties nevertheless. They are called EasyXXClientConfiguration. See e.g.
opclabs.doc-that.com/files/onlinedocs/QuickOpc/Latest/User%2...html#Setting%20Parameters.html . So, the COM developer just needs to instantiate e.g. an EasyDAClientConfiguration object, and he can then modify the global parameters.
In general, the developer is advised to set ALL these properties just once, and before calling any OPC operations. The reason for that is that only SOME, but NOT ALL of them behave the way you have described (i.e. the change will affect subsequent operations). For examples, process-wide COM security settings can only be set once in the process lifetime, and further attempts to change them are ignored by Windows.
To wrap it up, I think that the newer versions are better suited to what the customer wants, because each application settings are already isolated from others. The only downside compared to the older version is the absence of storage (such as config file or registry) for the settings, and the GUI utility to manipulate them – which is something I know about and is on the list, but not with high priority.
I hope this answers all your questions.