16. Changing from fleishigs to milchigs through hagoloh. Some hold one should not kasher his utensils to convert their status, e.g., kashering fleishige utensils through hagoloh to use them for milchigs from now on (מג"א סי' תק"ט סקי"א ). The reason is that since he is used to them being fleishigs, he can easily end up using them for fleishigs by mistake. Also, if one regularly goes back and forth between his utensils being fleishigs and milchigs through kashering, he may easily forget if he kashered them or not and make mistakes (שו"ת חת"ס יו"ד סי' ק"י ).
17. Parve dish that became fleishigs or milchigs. Even according to this minhag, if a parve dish or pot became fleishigs or milchigs by mistake, one may lechatchiloh kasher it to restore it to its parve status (יד יהודה סי' צ"ז סק"א ).
18. Changing an oven's status through libun. The poskim discuss whether this minhag is specifically for hagolas keilim (שער המלך פ"ד הל' יו"ט ה"ח ) or also for libun keilim (פמ"ג א"א או"ח סי' תנ"א סק"ל ). Thus, lechatchiloh, one should not regularly kasher his oven from fleishigs to milchigs lest he forget and make a mistake. Still, if there is a real need, e.g., on Erev Shavuos or during the Nine Days, when people cook lots of milchigs, one may kasher his oven once to milchigs, prepare all the food he needs to prepare, and kasher it back to fleishigs. Again, one should not do this regularly. Likewise, one should place a sign on the oven door indicating that the oven is milchig until its kashered.
19. Thus, if one always needs to bake or cook milchige food in an oven, it is worthwhile to have a small oven, e.g., a toaster oven, for milchigs besides for a regular oven for fleishigs and parve.
