Can we create custom objects in SRM standard content

Hi Experts,

We are working on SRM integration, imported the SRM standard content into ESR which have the standard DT/MT/SI.

Can we import or create the custom objects like DT/MT/MM/SI and OM in ESR under SAP standard namespace.

" http://sap.com/xi/SRM/Procurement/Global "

i have to send the data to third-party web-service. so i have to import the target message structure and do the mapping.

can we do this under the standard content?

Regards

Bhargava krishna