[Dx4win] Merging logs

[F6EXV]

Hi all !
Recently, someone asked how to merge different logs with different 
callsigns.
I have not seen a public response to this...
I have many logs under different callsigns used over the years (not only 
from France but from overseas as well) which I would like to merge, 
still wanting to see  which callsign they belong to... Like for example 
adding a note in the "Note for this QSO" field (only a potential 
solution , maybe there are better ways to do it)
Of course, the merge itself is quite easy to achieve, but how to 
diffenciate by callsign within the same master log ?
One reason by the way is to see if people will QSL for a rare or semi 
rare call, and not for a standard F call.... In other words, if I have 
worked K2XYZ from F6EXV and also from 7O8AA, how can they appear in the 
master log simultaneously, with an easy way to check (NOT the 
"selection", as I want them both to appear)
Thanks !
Paul F6EXV