I have a mid-2012 MacBook Pro into which I had installed an OWC data doubler SSD (removing the optical drive). I originally placed the SSD in the original HDD bay and moved the HDD to the data doubler bracket in the optical bay. I would like to switch these around (HDD back to its original bay). I'm assuming I should be able to switch the two drives around with no negative repercussions to normal operation - i.e. this should not require a reformat/reinstallation of the boot drive (which is the SSD). Would that be correct?
I don't think that will be a problem, but you may initially need to hold the Alt key while booting and choose the Startup drive. If it still won't boot, reset PRAM with holding altcmdPR while booting.
Just an FYI: I had a similar setup in a 2011 MBP. It worked great for a while, but I started getting disk errors on the drive in the ex-optical bay. I think the disk interface was just not designed for heavy use 😓