The lithium battery's internal temp rise is along the path of greatest power loss from internal resistance. Since P=R*I^2, the path of least resistance is not where the power loss is the highest but, ultimately very close to it since the current is a square of resistance. In any case, the greatest power loss is near the center of the battery and, by the time you feel the heat, the electrolyte that allows the electrons to be mobile will have been damaged. Typically over 200°C for a very short period can damage the organic salts used as electrolytes. Newer (mostly still-under-development) solid electrolyte (or molten electrolytes) can handle higher temps because they are elemental (like sulfur) or high temp stable and cannot easily be damaged. In any case, your over current tests are ok but likely damaging some of the electrolyte or internal packaging materials and shortening the life of the battery. Manufacturers set a specification for a reason and they are unlikely to set an "ultra safe" specification that you should feel free to violate with no reprocutions on safety and/or battery life because, a battery manufacturer needs to claim all they can safely claim in terms of battery performance because their competitor is claiming all they can claim. The overly cautious company would quickly go out of business because engineers and consumers want the highest performance for their dollar.
In other words, be careful about your design - it is likely decreasing battery life even if you don't feel temperature rise. Also, check the manufacturers datasheet - even consumer batteries have one from a good company like Duracell and the like. The datasheet may have short burst over-current allowances in much the same way some LEDs can be pulsed way above their rated current.