I was thinking about changing my index page. I wanted to alter the design a little, change my content (still on the same subject), add a couple keywords, and alter the title tag a little by taking one keyword out and putting a new one in. I would think that if I alter the title tag - my ranking in my niche would be ok since the niche and the KWs in the title tag still match. I'm just going for a higher ranking in an additional niche. I guess my question is - would all this change effect my ranking in my old niche?
you only change the index page or site layout if you must. minor change will not impcat on your ranking but layout and content change WILL make your ranking to flactuate. but if you have a stable ranking, then even if you change the layout and content, with some link building after the change will get you back up again