You can take too much B6, but the toxic dosage is much more than what you are talking about.
According to most web sites, B12 has no toxicity associated with it. However, when I got a hair mineral analysis done earlier this year, my cobalt showed up VERY high (6X the highest level shown on the chart). I got to looking to figure out why, and B12 is just bioavailable cobalt. My body was storing it. I found a website where a man who is experienced in giving B12 by IV was saying about 5% of people can store it in their body, and have side effects from having too much. A couple of websites that discuss toxicity symptoms have this to say:
"The thyroid gland may be enlarged with an excess of cobalt. Symptoms of a toxicity include paleness, diarrhea, fatigue, and numbness in the fingers and toes. A condition called polycythemia may arise as well. This is a condition where there are too many blood cells."
"some of them develop symptoms which may include coronary artery spasms with chest pains, numbness or pain down their right arm, while others experience TIA-like symptoms with tingling / numbness on the right side of the face, with either symptoms being at times severe enough to warrant a visit to the Emergency Room. There is also a risk of hypokalemia, pulmonary edema, peripheral vascular thrombosis, optic nerve atrophy for someone with Leber's disease, and others. Even without having had any Vitamin B12 injections, those patients who run naturally high Vitamin B12 and cobalt levels tend to frequently suffer from tachycardia, panic-anxiety attacks, or angina-like chest pains, that may be accompanied by numbness and tingling in the face or extremities."
I was having the symptom of tachycardia, and it got better after a while after I cut down on my consumption of B12 (had previously been taking 600% to 1200% of RDA per day). These sites said that the tests for serum B12 aren't reliable b/c your body is storing it in the tissue, you might show low on a serum test but actually have high tissue levels. This is similar to hemochromatosis for iron, just serum iron doesn't tell you a lot for that disease, same in this case. So, if you want to supplement with extra B12, there's a 95% chance it's perfectly fine, but just keep an eye out for any of the symptoms I posted above. If you want to try to find more info about toxicity, search for "cobalt toxicity" (minus the quotes) and not B12 toxicity, you get more info that way.