User blog comment:Sharple/OlexCraft/@comment-24558422-20121115020105/@comment-1917218-20121115152629

Use the magic launcher instead of the normal launcher. The regular launcher updates automatically, but the magic launcher will keep the jar file you want to use. The instructions are on this forum.

http://www.minecraftforum.net/topic/939149-launcher-magic-launcher-100-mods-options-news/