Is it permitted to deviate from yellow lines, during taxi?
There's no rule that you have to follow the lines, they're there purely as a guide, a reference for pilots to know where the center of the taxi lane is. Following it is at a pilot's discretion, to be deviated from at any point. Generally you follow the line because it's easy and it should keep you out of trouble, common reasons for deviating are:


Obstructions: vehicles, people, debris
Clearance: airplanes with large wingspans may need to hug one side of a taxiway to get around parked airplanes or buildings. In a small airfield you'll often have to get around a parked airplane or two