My Minhag is not to eat Gebrochts (Matza that has absorbed liquid). Could I be Meter Neder? if I can not why is it different then wearing a Gartel or wearing R"T Tefillin (that my father does)?

Shalom, Thank you for your question. There are two issues that need to be addressed – the first is - is there a good reason to change your custom, and why would you want to do so? The second issue is – if there is a good reason to change your custom, how does one go about doing so. In relation to the first issue – you did not explain at all why you would want to change your custom. This is important. Is this your custom from your parents, or did you start it yourself? Is it the practice of your community? Are you changing communities? Do you have a need to change your practice – perhaps for health, financial, or for reasons of shalom in your family? All these issues will have a weight in the answer to your question. (See Igrot Moshe, Orech Haim, volume 3, 64). Depending on the answers to the first issue, there are ways to change ones customs. Sometimes one needs to do Hatarat Nedarim (the annulment of vows), and sometimes even this is not needed (see Sharay Tshuvah, 460, 10). So – in short, the answer to your question is that it depends. Certainly there are cases when the custom of Gebrochts may be stopped – sometimes by annulment of vows, and sometimes even without it. In certain cases one would advised to continue their custom, and not change their practice, as even the customs of the Jewish people have great value. It will all depend on your exact situation, Blessings.