Piano wire will cut silicone yes. Sometimes if the seam is too tight to fit the wire through some very careful prying is necessary. a lubricant like WD-40 is helpful too. Be prepared to spend a whole day - it may not actually take that long, but don't try to rush it, it can be tricky.
Razor blades (changing out often), wire brushes and scotch pads (carefully so as not to scratch the glass), and acetone will take the silicone off but this is a big job not to be taken lightly. Getting old silicone off is a PITA, and again it is likely to take you longer than you expect it to. If you don't get all the old silicone off, the new silicone will not stick, and that's not a chance you want to take with a big tank like that!
Whenever I build or rebuild a tank I use DOW 732 or 832 to put it back together. It is several times stronger than regular hardware store silicone. The extra strength is really not required but it's nice to know that if you miss any spots getting old silicone off, or have a wide gap to fill that there's a significant insurance factor there with your seams.
Obviously you must provide pics if you do this!