GDS back to DEF/ MW DB

Hi, Here is a problem. Please bring in you ideas.

I have a GDS and netlist for a design but i don't have the placed and routed DB (DEF or MW) How can i convert the GDS and netlist back to MW/DEF.
The reason i need it is because i want to do some ECO changes to it and then stream out a GDS again.

Ro9ty