1] A fully-rooted android device.
2] Root Browser.
Here are the steps:
1] First of all keep in mind that this will work only if the phone is rooted. So if you are not, got ahed and search google on how to root your device.
2] Install and open Root Browser. Go to system/etc and find the file 'vold.fstab'. Make a backup of that file and save it there only( for restoring it if anything goes wrong ).
3] Open that file as a text file in RB text editor.
4] Find these lines: (the may vary from device to device)
dev_mount sdcard /storage/sdcard0 emmc@fat /devices/platform/goldfish_mmc.0 /devices/platform/mtk-msdc.0/mmc_host
dev_mount sdcard2 /storage/sdcard1 auto /devices/platform/goldfish_mmc.1 /devices/platform/mtk-msdc.1/mmc_host
5] Replace sdcard0 with sdcard1.
6] Do the same with next line. Replace sdcard1 with sdcard0.
7] Save the file and reboot.
I have tested this on my Micromax Canvas Juice, Xperia L and Samsung Galaxy S2, S duos2.
I don't think that there will be a fear of bricking the device because it is not releated very close to the system setting that need on boot. Try this you will be safe, but if you are not sure don't do that.