[old Chevy guy]

While its true that it won't affect the tuning if its out of adjustment and puts presure on the throtle plate and also the accelerater pump,it could cause it to flood or weep fuel. Another note if I remember right on a TH 350 when you manualy put it in 2nd it drives on the band instead of the drum and causes premature wear.I could be wrong. I worked at a transmision shop 19 or 20 years ago and even then I was only the installer.Not as hard as building them thats for sure,I took hundreds of those things apart for my boss but couldnt put one back together.Anyway thats what I think he told me once about 2nd gear,probably no big deal anyway if your not doing it every 5 minutes.