In LLBLGen Pro 3.5, what happened to "Create participating object subset"? I need to do some custom code generation for subset of entities

What's "Create participating object subset" ?

Check this part of LLBLGen documentation

http://www.llblgen.com/documentation/2.6/using%20the%20designer/designer_generatingcode.htm

You can see a button in the First "General Settings" tab called "Create participating object subset"

That's a feature that got removed from v3. You can accomplish the same thing by using rules. You can add a task and e.g. specify a where clause (using linq) which entities should be consumed for the task. you can also do this with custom settings (see SDK docs), and set for the group of entities you want to run a task for the setting to a given value, e.g. true, and in the preset, use a rule which dictates that a given task can only run if a setting X has a given value, e.g. true.