The metrics being collected for a model are impacted when you either add/remove a milestone or an indicator to/from the model.
The following is the impact in different scenarios:
If a milestone is added while metrics are being collected, new Integration Insight instances created after activation, will start collecting data for the new milestone. The existing metrics are unaffected.
If a milestone is deleted while metrics are being collected, the existing metrics collected for the deleted milestone are lost. The existing instance depict that the milestone was never reached. You will also get notified through a warning message about such changes upon reactivation of the model.
If an indicator is added while metrics are being collected, there is no impact on the existing metrics. The new Integration Insight instances will start collecting metrics for the new indicator upon re-activation of the model.
If an indicator is removed while metrics are being collected, the existing metrics collected for the indicator will be lost. On activating the model with a deleted indicator, you will be presented with a list of consoles where the indicator is being used. You must remove such consoles or remove the usage of the indicator from those consoles to proceed with activation of model.
For more information, see Impact of Model Reactivation After Changes in Model Metadata.