Yes there is a way. Select the first archive of the multivolume set in winrar (i used winrar 4.01 beta, the newest version as of the moment). Then go tools->convert archives (alt-q) in the archive types pane scroll across and select rar [it should have a (1) after it to show that there is one archive in that filter category]. Then you should see the first archive of the set appear on the left pane. Now go to compresion... button, choose type of rar and in the split size, enter your new split width. This is the basic new archive dialog exvept it seems the filename part is greyed out, it will make rar archives in the same folder with same name. This might cause a problem of file clobbering, so do this: if your existing archives are .part01.rar then select use old naming convention on one of the compresion... window tbs, and vice versa if your existing filres are .rar, .r0 etc IDK if winrar extracts to temp intermediately because i tested with a 1.5meg mp3 split into 128K chunks as part01.rar etc converted into 256K chunks as .rar, .r01 etc, and my computer done that instantly.
