I should have continued my post before becase its really not a super great idea especially if your first fermentation took a long time. Your yeast will go through 2 stages while fermenting. During its first stage it is multiplying and using most of its energy towards that and that is when oxygen is really needed hence an open primary or strring it to aerate your must, this is called aerobic fermentation. After a certain point you need to shut own or slow down this process and direct thier energy towards eating up sugar mosr and concentrating on making alc with little 02, this is called anaerobic fermentation. During thos last stage towards the end when yeast runs out of food it will tend to stress out and can cause off flavors and aromas, usually from lack of nutrient otherwise it just goes dormant. So if you put new wine on a one of these yeasts that is already stressed out its possible you could put more stress on this already struggling yeast even though you may have added more nutrient, once its damaged it may never recover. With all that said, if you have a good and fast fermentation your yeast can be in such good shape through all this that adding more wine onto this very healthy yeats colony can get your wine going much faster which is always a good thing.