HI Rezy,
I have read that from Hydro to soil is easy and no major complication but I have also read that some growers have found that hydro roots are not good for soil???
About transplanting from soil to hydro you must remove all soil from the root zone or you will create yourself a big problem in your rez, and your pumps, hoses, etc. When you remove the soil from the root zone be kind and moderate, you will also remove some roots but the plant will get back to its normal growth in a week or so
Peace