Download "Serby's cd-key changer" run it, chose new cd key, enter the name for a new cdkey, like key1.mpq, enter classic and lod cd keys, save. Do do that again but use key2.mpq as a name and ofc enter second set of cd keys classic and lod and save.
The 2 files shows up in your diablo 2 filder key1.mpq and key2.mpq and in that place u posted just enter:
u can just copy and paste that what i wrote
Than set - Game # CDkey - 18 (i have like that and its ok) but u can enter here whatever number u want.
Bot will switch cd keys after that number of runs.