Hi, On verge of purchasing a 2013 release 27" I7 IMAC with 3TB fusion drive. I will want to upgrade the drive to a Flash Drive in the future. Unfortunately cannot afford the top end spec with flash drive presently so want to do it as an upgrade in the future. I have noted that it is possible to do this as a DIY job - but I would have no confidence doing it myself. My questions; Is it possible for this to be done by a Apple reseller - and if so, how much would it cost (assuming I sourced the flash drive myself). Based in UK. Thanks.