Applying new ESS SP during Development

Hello,

I am on EP7.0 ERP05 NW04s ESS 600 SP 8 Patch 9 and making modifications to the ESS standard code using NWDI , now there is one new functionality delivered in the new ESS 600 SP9 which we need to apply .....without losing the changes done till so far .....now what's the procedure to apply this new SP to the Development System using NWDI...?

Any help would be highly appreciated.