I understand, that's one of my warning. Calibrating if you're on a rush for a batch isn't good. I'll be honest with you, calibration (following my step by step instructions) should take you 2 hrs max.
The "collateral damage" of calibration is that you might have to correct some of your placement programs, if you tweaked them to work.
If you didn't modify your programs and you just accepted some offsets because they correct themselves during baking, then you'll have only positive results and benefits from calibrating.
In any case I just suggest to BACKUP at 100% the luna-win directory on your HD. I do have several version of the software in the same directory, the .EXE files being just named differently, that's how I moved progressively. But I snapshot the state of my machine with paranoid massive backups of the "whole thing" including data / placement programs. Just in case.
2.1.23 won't change your part definition. Look at the change log (extract the archive in another directory), it's mostly about bug corrections and a few addition.
The MAJOR change in the placement is the tray orientation angle. See the recent bug corrections (most of those moved the versioning from 2.1.18 to 2.1.23 IIRC).http://forums.adafruit.com/viewtopic.php?f=42&t=32724#p162097
Check that same thread post #11 for the explanation of the new tray angle system (which makes the tray working exactly like the feeders now, for then angle settings). If your trays always had an angle 0°, it won't affect anything in the placement program but if you had some assymmetric TQFP parts in tray, you'll have to double check your program.
I'll get the missing corrections of the manual by monday only (sorry for the delay). It was overall quite fast to apply them to the document, expect the PDF on tuesday. You'll need to free one of your afternoon (or so) to recalibrate the machine. If yours is working already (aside of alignment problems, calibration will be just fine tune. 2 other users here seem to have massive problems but it looks like they have either a lot or 100% of defaults values in their constants.
I would love to see your Posi2 calibration, if you would snapshot and post that (nozzle extender menu, edit mode, posi2, F8). To check what sort of "stroke" depth you have there (it's defines the focus of the head to the bottom camera), to compare with mine and theirs as their setup looks WAY off. Thanks !