When the reason ceases, the prohibition ceases
If the factor that caused the prohibition no longer exists, there is no longer justification for the prohibition.
(“Rather, the reasoning is clear and well explained in the words of the Rosh and the halakhic authorities, for this is not comparable to meat cooked with milk, since there the prohibition exists only because it imparts flavor; therefore, when the flavor is nullified, the prohibition is nullified.” — Shakh, Yoreh De‘ah, §299.)
Translation
Expression (Hebrew)
בָּטֵל הַטַּעַם בָּטֵל הָאִסּוּר
Definition (Hebrew)
אִם הַגּוֹרֵם שֶׁהֵבִיא לָאִסּוּר אֵינוֹ קַיָּם יוֹתֵר, הֲרֵי שֶׁאֵין יוֹתֵר הַצְדָּקָה לָאִסּוּר.
("אֶלָּא הַטַּעַם בָּרוּר וּמְבוֹאָר בְּדִבְרֵי הָרֹא״שׁ וּפוֹסְקִים דְּלָא דָּמֵי לְבָשָׂר בְּחָלָב לְפִי שֶׁהָתָם אֵין הָאִסּוּר אֶלָּא מִחֲמַת שֶׁיִּתֵּן טַעַם וְהַלְכָּךְ כְּשֶׁבָּטֵל הַטַּעַם בָּטֵל הָאִסּוּר" – שַׁ״ךְ יוֹרֶה דֵעָה סִימָן רַצ״ט)