Q. I usually split my maaser money to donate to different institutions. On this occasion I had first in mind to give it all to institution A, can I change it and give it now all to institution B? Nothing was verbally said.

A. Remoh (Y.D. 258: 13) rules that one becomes obliged to give to charity just by committing himself in his mind to donate. Although, there are dissenting views, as the Shulchan Aruch rules (C.M. 212: 8, see Piskei Teshuva Y.D. ibid. et.al.) one should be stringent when there was indeed a real serious commitment, even if only on ones mind. Therefore, as mentioned in the prior question Horav Shlomo Miller Shlit’a advises that one should always perform the declaration mentioned therein.
If that was not done, the Rov maintains that if one had indeed a serious commitment in one’s mind to give to an institution and then decides to change the beneficiary, one should follow a hattoras nedorim process in front of a beis din, similar to the one done on Erev Rosh Hashono.

Rabbi A. Bartfeld as revised by Horav Shlomo Miller Shlit’a