I'm new to this forum but I thought I would throw in my 2 cents.

You might want to ask your LBS if they would swap cranks out prior to your purchase. They may offer to do this for free (I know most do if you want a different cassette), if not, they may offer credit for the existing one and you may have a slight upcharge for the compact - it never hurts to ask.

That said, the Standard Double crank's chainrings have a 130BCD (Bolt Circle Diameter) which means the spacing for each bolt is 130mm apart verses a Compact crank at 110BCD. Still, you can install a 50T chainring on a standard crank (FSA sells one) however the smallest chainring you can install is a 38T. I am currently running a 50/38T on my standard cranks and loving it.