freeze design in one portion of the chip and modify another using Soc Encounter

Hi,
I am taking over a design from a colleague which has already been placed and routed. Some of routes have been fixed by hand on one section of the chip to ensure they are DRC clean. I would like to fix (freeze) the design (blocks and top level routes) on this section of the chip and rip out the rest, place and route them again. The section that needs to be fixed contains custom blocks. I am using Cadence Soc Encounter.

I would like to know if there is any way to cut a portion of the chip, mark the nets that cross this boundary as pins. I would then like to place and route the rest such that they route to the newly formed pins while maintaining the existing routes over the fixed section of the chip. Can this be done in Soc Encounter? If so, can you please point to the steps that need to be done.

If not are there any other ways of getting this done (place and route one section without disturbing already routed wires in another)?

Any help is much appreciated.

Thanks,
vatsan

You can select all the nets in an area by for example - dbGet top.nets.box ...
then put them under "fixed" attribute.
Then you can continue with you other routing.