Antennas don't work that way. The length of the antenna is proportional to the frequency (wave form, in height) being eminated from the transmitter. Adding wire to your antenna will not give it better range.

Only if you switched frequencies (IE, went to a different FM frequency such as going from 72 mHz to say, 35 mHz, which you wouldn't), you would theoretically increase your range.

If you cut your antenna wire and make it shorter, you're essentially eliminating the frequencies the receiver was designed to pick up. Although if you switched the transmitter to a higher frequency, say 100 mHz, it would pick the signal up, but at a lesser range.

MPB