I think some more info is needed here but you can always stunt their growth with cold temperatures and/or SO2. Dry ice is the "best" thing to use to chill down the wine/juice/fruit but you could get creative with other methods of chilling. I'm assuming you're planning on using SO2 in some form to "kill them" but you could also put some KMBS powder on top of the fruit after it's been picked, it's not the ideal way to do it unless you can really get the fruit all mixed up but it's better than nothing. If you go that route, make sure you check SO2 levels before adding more to the pressed wine/juice because theoretically most of that KMBS powder will dissolve into your juice/wine. If this is a red wine, this is what many people would do anyways.
If you added commercial yeast, chances are it will out compete the natural yeast. Once fermentation is complete (all the sugar has been converted to alcohol), there is no food for the yeast, commercial or natural, so they will not be active. You will need to add so2 for preservation purposes, but it will not have an impact on the yeast at that point.