Prevent User from Overriding Expense Report COA

We want to prevent end user from modifying the main account in their expense report COA.

We did some research and found the below solution (which is somewhat still lacking).

1. If the profile option EXM_ALLOW_FULL_ACCT_OVERRIDE is set to Y, then user is able to modify the entire COA segments.
2. If the profile option EXM_ALLOW_FULL_ACCT_OVERRIDE is set to N, then:
   1. If user has a role which has a privilege EXM_OVERRIDE_EXPENSE_ACCOUNT_ALLOCATION_PRIV, then user is able to modify only 2 segments: company and responsibility center.
   2. Otherwise, no segment can be overridden. The default COA will be used.