The pasuk towards the beginning of Matos:
derasha in which it has the meaning of mechilah, they also interpret it (in Sifrei) as coming from the root ch-l-l. Thus, he should not profane his word.
Rashi endorses that reading:
he shall not violate his word Heb. לֹא יַחֵל דְּבָרוֹ, like לֹא יְחַלֵּל דְּבָרוֹ“he shall not profane his word,” he shall not treat his word as being unholy. — [Sifrei Mattoth 8]And Siftei Chachamim offers his analysis of how this works out.
Ibn Ezra also endorses this explanation and rejects mechilah. I am not sure I understand, or agree with, his further point.
Then, we turn to Rashbam. I messed up in the image above, so here is a better clip. We see him state that those who explain, on a peshat level, that it means chilul, are mistaken. It would seem that he is targeting Rashi and perhaps Ibn Ezra as well. It would seem that he will allow it on the level of derash. He does not endorse mechila but rather y-ch-l as the root, it would seem, and that root means to delay. He gives examples. Thus, to offer some examples:
|י וַיָּחֶל עוֹד, שִׁבְעַת יָמִים אֲחֵרִים; וַיֹּסֶף שַׁלַּח אֶת-הַיּוֹנָה, מִן-הַתֵּבָה.||10 And he stayed yet other seven days; and again he sent forth the dove out of the ark.|
neder, which is to bring an offering, where elsewhere we have bal te`acher. And כְּכָל-הַיֹּצֵא מִפִּיו יַעֲשֶׂה goes on the shevuah.
Talk of peshat vs. derash always makes me curious to see what the Karaites have to say on it. Aharon ben Yosef the Karaite endorses chilul, and says that whoever suggests not delaying - lo te`acher -- is making an error in dikduk, because the yud is not a radical here, but rather designates the future tense. The supercommentary says this is addressed to a different (perhaps Karaite) commentator, but the same would apply to Rashbam.
Perhaps Rashbam could claim that it is neutral (=what we normally call "present") tense, but passive, something like the kal passive. Especially is we are allowed to revocalize.