A similar question is the subject of much discussion in YD 228. Rav Moshe Stern, the Debreciner Rav, in Shu"t Beer Moshe Chelek Gimel, Siman 163-165 (which includes the summary of his answer), was asked about a person who promised never to bring a TV into his house, and now wanted him to be Matir his Neder:

Basically his answer is that it is Assur to be Matir such a Neder, and it is based off of his understanding of the Poskim in the Sugya (it's important to see Tur/SA/Rema 128:16 and Nosei Keilim on all of that). His main decisions are based on the Shu"t Rivash 43:2 (copied below), although there is some room for Heter in certain cases based off the Shu"t Rema 103. All of the discussion revolves around being Matir a Neder not to do a prohibited act, with the classic example being Mesachek Bekubiya, or gambling.
... אבל שבועה שנעשית למנוע מאסור אין מתירין אותה. ושחוק בקוביא, הנה יש בו אסורא דרבנן, כדאיתא בסנהדרין פרק זה בורר (כ"ד:). ואפילו לרב ששת דס"ל התם דליכא אסמכתא בקוביא, מ"מ דבר מכוער ומתועב ומשוקץ הוא. ורבים חללים הפיל ועצומים כל הרוגיו. ומפורש הוא בירושלמי (נדרים פ"ה ה"ד) דמי שנדר שלא לצחוק, אין מתירין אותו. וכן דעת הרמב"ן ז"ל במשפט החרם שלו וכ"כ הרשב"א ז"ל בתשובה...
After the fact, he brought the Orchos Chaim (Hilchos Shevuos Unedarim), who says that according to Ramban and Semak it is Assur to be Matir a promise not to gamble, and even if he is already gambling, we should fine him and place him in "Nidui":
...מי שנשבע שלא לשחק בקוביא, אפילו עבר כבר על שבועתו אסור להתיר לו כדי שלא יהיה חוטא נשכר, אלא יש לנדותו ולהבדילו עד שישים קנס עליו ויקבל על עצמו שלא ישב במקום המשחקים...
Based on the sources brought within and the Pesak above, in our case it would be Assur to be Matir Reuven's Neder not to eat pig. Both of points 1 and 2 from the question seem to be addressed in the above Teshuva, and the answer is not to be Matir this, for these reasons.
If someone was Matir this Neder, that is a separate Halachic discussion as to whether it is valid, and not the topic of this post.
For MY users that appreciate "easter eggs" in Shu"t Sefarim, it would be worth it to read the final two paragraphs of his Teshuva, Beer Moshe 165:12.