It is an worst decision. It will create lots of inconsistent and you may not face any problem for now, but you will face problem later.
No-one can't say how much internal tables are related to table EORD. When we update anything from transaction or function module, system updates all internal tables also. But if you update any table from direct table edit, then system can't update these internal tables.
For your optimistic, SAP is removing this direct editing option, read this OSS note 1420281 - CO-OM tools: SE16N: Deactivating &SAP_EDIT
There are many discussion exists in SCN, if you search for keyword "mass change source list"