Do you mean your gonna like add a table named custom items that works just like items?
if so its very easy =P

The table has to be the same exact structure as the items table frist off

Thennn you open world.conf



Ctrl+f
LoadAdditionalTables="">
and add the table inside the ""
(for more than one table you separate with commas)


(Not sure if this is in old versions but should be =P)