If you are talking about feeding the right dilution of the right food too often, then nothing will happen, most of the feed will drain out of the basket. Eventually you might change the soil ph but if you change the basket soil every year then no problem. Nothing much will happen if you give the wrong feed but if you don't give ericaceous feed to ericaceous plants (acid soil plants), then the leaves will yellow.
If you put the wrong dilution in and the feed is too strong you will speed up the changes to the soil but even so over over growing season shouldn't be a problem. If you pour it in neat then you might burn the roots and kill the plants but still unlikely.