I have attached two patches from bug 582051 that are intended to make --skipcopy more useful for testing. One is for functionallity, the other expands the documentation of what skipcopy skips a bit better.
As discussed in the bug report I don't like:
+if [ -s $USBMNT/$LIVEOS/$OVERFILE ]; then
and think that it should be:
+if [ "$overlaysizemb" -gt 0 ]; then
This is easier to understand and seems more likely to be correct. I am not sure if my comment about my suggestion was misunderstood, but I don't see why my suggestion wouldn't work and the one provided would. But maybe there is something subtle going on.
Since --skipcopy is for testing I don't think the patch will have much impact on normal use.
So I would be inclined to except this patch if modified as I suggest, but I'd like to get more feedback.