the IDs remain the same - if a tile with the same ID exists, it will be overwritten (essentially that is what the client does with the verdata on-the-fly)
OSI updates won't work anymore, but is this really a concern? If you use verdata, you can't have the most recent client, so updates are no option anyway

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RunUO RemoteAdmin - Control your shard remotely and keep an eye on the page queue
MulEditor - Modify gump, art, tiledata, multimap, localization files and
map/statics.
CentrED - A Client/Server based
multi-user map editor.