Hi Naomi,
>Anyway, I think gather works quite nice instead of building the replace command (though I considered it as well at first).

I responded to the "efficient" part, since that is mesurable.

For me, abstacting the logic into a string has other "nice" possibilities, for instance easy logging with strtofile(). Elegance is probably largely in the eye of the beholder: Using a scatter - approach I'ld probably just (scetchy pseudo)

scatter name loSource
loEmpty = createobject ("empty")
for lnRun = 1 to aelements(laProp,,,)
  if empty and ...
    addobject(loEmpty, laProp[m.lnRun], eval(laProp[m.lnRun])) && in a loop across the changeworthy properties,  
  endif
next
gather name loEmpty

from this already "pruned" object.

This way might actually be slower than Sergey's way, depending on the speed of addproperty in a loop vs. a single gather operation - not tested <g>. But for me the "elegance" would be in the possibility to log ONLY the resulting changes by iterating over all the properties of the previously "empty" object. As I said, in the eye of the beholder <bg>.

regds

thomas