Certainly can, however, are the original wheels bad ? an S2 is not a special size, and will fit any modern 20 x 2.125 or large 20 x 2.25,2.35,etc....... S7 front is special size, only available aftermarket as a , iirc, a Kenda ? Amazon ( Niagara Cycle ) had them I think.
If the rims are good...