You can define UI MetaModel entries in the same way as you do in MPT. Please refer to the section called “UI Metamodel” for more information on UI MetaModel.
The only difference is that both SPT and EPT entries share the same namespace. This means that if you have a WebAction or any other entry in the SPT and you have the same entry in your EPT by the same name, then the EPT entry will "override" the SPT version.
Also, any ref entries (WebActionRef/WebActionGroupRef) in the EPT without a module prefix will search the SPT and then the EPT. To reference something from an MPT, you must provide the module attribute.