User blog comment:Parax./MC Help/@comment-1917218-20121220210229

Well, you can download the Minecraft Magic Launcher for this.

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

Just download on this link and open the file, then go to settings and choose those Minecraft.jar file and it should use that one. http://assets.minecraft.net/1_4_5/minecraft.jar

When you want to update to 1.4.6, use this Minecraft.jar http://assets.minecraft.net/1_4_6/minecraft.jar