Rav Moshe Shternbuch - Being Meikil When You Were Always Machmir
If you are Machmir on a specific Chumra three times you may not be Meikil unless you are Matir Neder. The reason is because doing something three times is tantamount to promising you will always do it.
There is an exception to this case says Rav Moshe Shternbuch (4:207). If you want to stop being machmir from here on then you need hataras Nedarim. However if you need to be Meikil at a specific time or because of a specific event you need not be matir neder.
The Mekor for this is the Dagul Mervava (YD 214) who says that if there is a certain day that you are noheg to fast as a chumra and he finds himself attending a Seudas Bris Mila and he would like to eat, he may do so without any hatara. The reason is that he is not trying to end his chumra and his minhag will continue to remain intact. He only wants to make an exception for this event and he never intended to be machmir is such a case.
Important Note: We bring this tshuvah as a starting point for discussion and not to convey any halacha. We try to convey the Tshuva to the best of our ability. We admit that our understanding may not be accurate. One should learn the tshuva to verify the accuracy of our interpretation. Please understand that this Tshuva may not be the final word on this topic. One should consult a Rav before drawing any conclusions.