Process authors can use Activity Variability to customize an existing activity.
Select any activity's properties view. Here, select 'extends' in variability type drop menu and click select button. In the filter chose any acitivity you want to extend. Once you select, in WBS the selected activity and it's descriptors are displayed in green. In configuration explere, you can see the extending activity and in browsing extedning activity and its descriptors will be displayed.
Select any activity's properties view. Here, select 'contributes' in variability type drop menu and click select button. In the filter chose any acitiy you want to contribute to. Once you select, go to browsing to see the realisation. The activity being contributed will disappear from configuration explorer. And on the right side of browsing, the descriptors of that activity will display under the activity that is being contributed. If the contributing activity has a sub-activity then, it will appear in green color under the activity being contributed in configuration explorer.
Select any activity's properties view. Here, select 'replace' in variability type drop menu and click select button. In the filter chose any acitivity you want to replace. Once you select, goto browsing to check the realisation. Both in configuration explorer and in right side browsing, the activity being replaced will disappear and you should see the activity that is replacing in that place.