Hi Bin,
->Can I modify another object's value?
Yes, as long as they are in the same deployment unit.
You can query or retrieve an instance of a business object and assign its elements (PSM released fields and extension fields).
There is one limitation where you can getan error message like ESI_COMMON _107 something.
It means that the instance you are trying to update is in "Read-Only" mode because of its status.
e.g "In Approval", "In Process" , etc.
Best Regards,
Fred