Crisco should freeze at about -4° to -10° F (-20° to -23.5° C) or a little lower. But freezing will not stop it from going rancid, but if properly packaged can retard the oxydation rate.
Put the room temp Crisco in "freezer" grade plastic bags and squeeze out as much air as you can (to remove as much of the oxygen as possible) and then seal. This is basically a 2-point chemical reaction - oxydation requires oxygen and heat - the more you can remove of both, the slower the reaction. This will not stop oxydation (fat going rancid) but it will retard it a bit. Sorry scott123 - Crisco doesn't defy oxydation - it simply retards it due to hydrogenation ... which is where Trans Fats come into play - and gets into a chemistry discussion we've already had.
Now - as for substituting butter for shortening ... yeah, you could - if you're willing to accept the changes in texture. Butter has a low (and very narrow range) melting point - shortening has a higher broader range melting point. In something like cookies - replacing the shorting with butter in a cookie recipe will result in a cookie that spreads more, is dryer, flatter, and crisper. In cakes - it can mean a difference in the moistness, texture and tenderness of the crumb. In something like a pie crust - if you want both flakey and tender - you need both butter and shortening.
Put the room temp Crisco in "freezer" grade plastic bags and squeeze out as much air as you can (to remove as much of the oxygen as possible) and then seal. This is basically a 2-point chemical reaction - oxydation requires oxygen and heat - the more you can remove of both, the slower the reaction. This will not stop oxydation (fat going rancid) but it will retard it a bit. Sorry scott123 - Crisco doesn't defy oxydation - it simply retards it due to hydrogenation ... which is where Trans Fats come into play - and gets into a chemistry discussion we've already had.
Now - as for substituting butter for shortening ... yeah, you could - if you're willing to accept the changes in texture. Butter has a low (and very narrow range) melting point - shortening has a higher broader range melting point. In something like cookies - replacing the shorting with butter in a cookie recipe will result in a cookie that spreads more, is dryer, flatter, and crisper. In cakes - it can mean a difference in the moistness, texture and tenderness of the crumb. In something like a pie crust - if you want both flakey and tender - you need both butter and shortening.