As the name indicates, After Create Rule gets executed after an account is created.
You can make use of After Modify Rule to do that. You can have some entitlement specific to this homedrive, maybe a dummy group no access assigned to it. Using this Group, you can execute logic in PowerShell script to manage homedrive.
My requirement is , It should not be modify or create homedrive/Exchange when AD is already exist in Native application However, It is getting modified when AD account is already exist in native application.
In that case within your script please add a check to verify existence of AD account first. Only if account is not found, the rest of the script should execute.
You might be having Homedrive/Exchange script only in After Create Rule. If yes, then this Rule will be triggered only when an account is created. This won’t trigger again if user has AD account already unless some correlation issues. AD account is not in identity cube, maybe in uncorrelated accounts.
You can find error in Account Request (I believe so), which is input to your PowerShell scripts. You can stop the execution if there is any error.
My understanding was, After Create Rule will trigger only if account creation is successful. But it is not. It will trigger even if it is failure.
Instead of focusing on stopping the Homedrive/Exchange script execution, troubleshoot why this is happening in the first place.