Not a problem. There are a few things you can do. You can always blanch the sliced radishes for a few minutes and then plunge them into an ice bath to immediately cool them. This will take most of the peppery flavor out. Second, you could replace the red radish with thinly sliced daikon radish, or for a very neutral flavor, try water chestnuts. Lastly, you can leave them out of the recipe but the added crunch that the radishes bring to the dish is wonderful!