Change Immediately option is not available for Activities in your Project under Overview view in Business Configuration workcenter.
Reproducing the Issue
1) Go to Business Configuration workcenter
2) Go to Overview view
3) Select Open Activity List
4) Select any activity e.g. Quantities and Units of Measure
In the given scenario the reported tenant is a Test System and it is connected to Productive System and there is already a change project copied from Productive system and this change project is the main workspace.
If you want to perform any changes to a fine tuning activity, then activity should be added to the change project and then you can perform the changes.
Note: Saved changes will be visible only in the Test system until you trigger merge. After merge, changes will reflect in production system.
KBA , SRD-MD-OM , Organizational Management , How To