If you have state that should persist between generator runs, e.g. to parameterize generators, a good solution is to have that information as properties in the model, e.g. of the top level graph from which the generator is run. To separate these parameters from the top level graph, you can store them in a separate graph type which just holds the parameters and a link to the top level graph.

If the parameters are temporary, you could use prompt...ask. If the parameters are per user, and should apply to all generation for that user, you could use text files in the working directory, read with filename...read and assigned to variables as necessary (a regex translator could easily separate the left and right parts of a line in .ini file format).