The Gemara on 9b states that it is permissible for a woman to put "seed" on her face on Chol Hamoed, despite the pain which should be assur, because she will be "m'sameach l'achar zman". Do we see anywhere else that simcha later permits us to do something that would otherwise be assur? Why don't we say, for example, I can do hachana on shabbos, becuase it will give me simcha for after shabbos? What is the geder of this kulah?
Ari Rosenstein, Ramat Bet Shemesh
There is no reason to prohibit a women from placing lime ("Sid") on her face during the Moed other than the pain and discomfort that it causes her. In such a case, we can permit the act if, in the final analysis, it brings her more pleasure during the Moed than pain - for instance, if it will make her more beautiful during the latter part of the Moed.
A comparable Halachah would be allowing a person to fast a Ta'anis Chalom on Shabbos even though one suffers discomfort at the time, since all things considered it will cause a person Oneg on Shabbos, knowing that he has fasted and detered punishment (OC 288:4). (An opposite application of the principle, with regard to collecting a loan from an Oved Avodah Zarah can be found in the Mishnah, Avodah Zarah 2a.)
In the case of Hachanah, the prohibition is not related to discomfort and besides, the comfort is not realized on Shabbos.
Be well,
Mordecai Kornfeld