Topping Up Soil

This might be a very dumn question, but I'd rather sound dumb than risk hurting the garden I've recently inherited. The garden is a rather neglected raised bed that needs a good 6-8" more soil added, which I meant to do in the winter. Is there any risk to the plants if I top the garden up all the way now that the plants are sprouting for the spring, or should I top up in incements isntead? It's mostly peonies, hostas, bee balm and black eyes susans in there, with the peonies being my primary concern.