You may have been faking the statistics information (e.g. cardinality) for nicknames to influence Optimizer to generate a specific plan. However, please note that, you might see that the plan generated by Optimizer gets changed when you enable the Automatic update of nickname statistics feature or migrate to Federation Server V9.5 with default setting. It in fact results in the fake statistics getting reset by the automatic feature.
When the Automatic update of nickname statistics feature is enabled, the NNSTAT stored procedure will be run automatically, and set new values in statistics catalog tables. Since this feature is enabled by default in Federation Server V9.5, you may see it happens when migrating to this release. Please refer to Information Center for how to disable or customize this feature.