If it is within the 20 campaigns limit, you can add new campaigns to an existing OptiGroup. You can also remove campaigns from an existing Optigroup as long as there are at least 2 active campaigns for Optily to optimize against. Both of these changes have a few consequences:
If the new campaign does not have any primary goal conversions on a non-weighted goal, Optily will move to a lower level of Optimization for the budget recommendations.
If the new campaign does have primary goal conversions, the ranking might change. This would affect the next budget recommendation generated.
If a campaign is removed, the ranking will be reset and the next budget recommendation will be based on the remaining campaigns only.
The OptiGroup reporting will show a combined report before a change was made and after.