what r changes u can apply on iges or step file other than extracting surfaces??
For thickness you can change it with "Thickness" command as positive or negative. But for diameter and radius u cant. For these you can follow that step. Firstly for hole and cylindirical pocket. Create a sketch on the surface and project the curves and make them construction. then create point/points on the center of circles (if they are patternable you dont need do this for all) and exit sketch. Run the "Romeve Face" command and delete the surfaces which you want. And recreate them with new value.
Secondly for fillets. Run the "Romeve Face" command and delete the fillets. And refillet with new value.
In addition you can resize hole diameter with Thickness command if you select circular face.