You can allow users to change task state only and deny to change anything else by adding three permission rules.
The first permission rule lets users begin editing all task properties.
The second permission rule denies users to end editing all task properties except for the State property and the Remain property which depends on the State property.
The third permission rule allows users to end editing the State property.
Tip If you want to allow users to edit more task properties such as Notes, Comments, you need to remove this property from the filter condition of the second permission rule and add this property to the filter condition of the third permission rule.
To apply your permission rules to certain users or groups only
2. Hold down the Ctrl key, while clicking the old rules that conflict with the new rules, right-click the selection, select Edit, click the Users and Groups tab, and then select the check boxes next to users and groups you want to exclude.