In coming back to this topic in 6.4.3, I note the following problem situation:

Earlier, using 6.2.1, I had allotted 1160 or so for persistent storage, leaving
a few unused Mbs on the SD Card. In 6.4.3, I allotted 1181, leaving no unused Mbs.
What worked before as a backup scheme isn't working for me now.

Saving the img on Win7 and attempting to replace imgs did NOT work.
The process won't complete, because the SD Card has too little space.
Perhaps the imgs are a bit larger in ntsf than in FAT32.

Trying to do the same img replacement game in a Knoppix CD environment also
did NOT work. The process completed without complaint, but the persistent store
no longer worked at all.
There may be some small overhead requirement even here.

I haven't heard any independent complaints, but I'd suggest those interested
leave around 10Mb's unused in their persistent store operation if they intend
to rely on this switcheroo scheme.

More on this whenever I have to rebuild my current 6.4.3 setup.
Any useful comments in the meantime are welcome.