I do this with my house blend of Cali Ale Yeast and Koelsch yeast. They do tend to "drift" over multiple generations (mostly because of differences in flocculation and alcohol tolerance), but the effect is fairly subtle for the first few generations when repitching onto the yeast cake or harvesting/washing the yeast. Building it up from the bottle is likely to increase the odds of one yeast becoming dominant over the other because of the very small sample size and relatively harsh environment they are in, but this being a second generation harvest, it'll probably be perfectly fine.
Cheers, and good luck with your experiment!
The Fiesty(sic) Goat Brewery est. 2007 & Clusterfuggle Experimental Ales est. 2009
Planned: sLambic II, Flanders Red II
Primary: Fat Man Porter, Orange Blossom Mead, sLambic I
Secondary: Flanders Red I
Kegged: 3 different ciders, Janet's Brown, Barrel-aged Stout, Hallertau Blanc Pale Ale
Bottled: Flanders Red I