What if Flynn/Eugene cut Rapunzel's hair a little bit longer,will it have an effect on Gothel? And do Du think Rapunzel's hair will be long again?

It will affect Gothel, of course. Even a single strand Du cute from her hair.. BOOM! GOTHEL IS AFFECTED AND TURNED OLD! Even though how long Du cut it, it will still affect Gothel, remember that time when she was still a baby? And I don't think Rapunzel's hair will be long again. When she was still a baby, the strand Gothel cut from her hair never grew back.