Why do the Litvishe gedolim, such as the Gaon of Vilna and the Chazon Ish, hold that there is no inyan to eat matzah on Pesach Sheini, while the minhag of all Chassidim is to eat matzah? Is it because the Litvishe gedolim are concerned about baal tosif, as someone might eat the matzah with the intent that he is doing a mitzvah?
Regarding one who has no minhag in this area, how should he conduct himself? (There are also different opinions regarding when the matzah should be eaten, if it is eaten at all.)
The idea of eating matzoh on peach sheini is not brought in halacha, therefore they didn’t do anything about it in this way. The Gaon didn’t eat matzoh after pesach to show that he is only eating it when it is actually a mitzvah. This is not because of baal tosef, rather his own personal doing. Besides, even those who do it, don’t say that it is a mitzvah in the torah to do.
If you don’t have a minhag about this, you can do whatever you want.
Bikas Hapesach 17-6, Luach Davar B’ito 27 Nissan