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RTC 5.0.2 - Can I defined read only on attribute in specific state?

Accepted answer

You can configure a precodition "Prevent Editing", where you can define attributes that can't be changed in a specified state.
Check this:
https://jazz.net/help-dev/clm/index.jsp?re=1&topic=/com.ibm.team.workitem.doc/topics/t_defining_precond_fuactions_web.html&scope=null
One other answer

You can go to Operations behavior (RTC eclipse client) or Preconditions and Followup actions if using Web interface. The steps vary based on which interface you use.
For Eclipse client go to Process Configuration>Team Configuration>Operation Behavior>Select the Operation (save Work Item) and User role(s) you want to be affected by this change and add the precondition called Read-Only attribute for Type and State. You can then select what attributes are read only in any given state.
I attached an image explaining the steps numbered in red.