I think and I have also noticed that if you detune/retune a string sometimes, that affects its characteristics considerably.
So I try to avoid this process. But if for example you do it only once, in order to "play in" a string to have it as a good backup, I guess that this affect would be minor.
Paulino Bernabe Especial 2009
Ramirez 1A 1980
Alhambra Luthier india 2012
Panagi Brothers 1970
Juan Martinez nr 55 2014 (the comeback)
Yamaha cg 110 1988 (the 1st)
2014: the comeback