Agree with previous comment.  I have never heard of anyone trying to require this.  Ask them to show you the source for their requirement, e.g., where is the ANSI reference?

I found the following in MIL-HDBK-881, Work Breakdown Structures:

3.1.4  Control Account Level. To provide the responsible contract manager with technical, schedule, and other needed resource information, the management control system must be keyed to the same WBS element and organizational unit. The WBS level at which the management control system is established is primarily a function of the magnitude of the program and the type of product required by the contract.  The responsible organizational level is a function of the company’s management span of control and upper management's desire to delegate the responsibility for WBS elements to lower management levels.  In identifying control accounts, the contractor is expected to establish organizational responsibilities at meaningful and appropriate levels. Otherwise, the contractor's existing management control systems and responsibility assignments may be affected adversely.
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The guidance has always been to allow the contractor to establish the CA level at the most meaningful point for management.

Let me also add by definition, every work package within a single control account will be at the same level.  It all depends on where the control account level is established.  I'd also like to add that the control account should be established at the lowest level of the WBS, since there is a requirement that the control account be established for a single WBS element and only one element.  You can have work packages below the control account level with unique identifiers, but the "official" WBS numbering ends at the control account level.

Don't understand their requirement to "rework" completed effort.  Seems contrary to the ANSI requirement to control retroactive changes.  You can map to alternate WBS structures in wInsight, but I would challenge this requirement.