Hi Shamil,
Yes you can absolutely do this. We call this a squeeze back and it requires the use of a DVE. You can do this on the main PGM ME but it might be simpler to do it downstream using a MiniME.
Using a MiniME simply assign a DVE to key 1and the lower third to key 2. Assign PGM from you main ME into MiniME key1. you will need to assign the MiniME output to where PGM is currently. Now you can adjust the size and position of PGM using MiniME Key1 DVE. If you combine this with Effects dissolve memory recalls you can create events where the PGM background can be automatically 'squeezed back' when key 2 is on via use of custom controls.
Wherever you decide to do this depends on your workflow and PGM composition, but the principle is the same regardless. Simply use a DVE to scale the video image on a key layer under the lower third.
#Carbonite