Make some new character designs using the advice. Then compare them to the original characters you sent off. If the new ones are better then use those and if the old ones are better than use those. This way you're not any worse off than you were at the beginning, and maybe better.
I had this happen to me once and what I did was redraw the picture in a completely different style, incorporating many of the suggestions for colouring but not copying or using the other person's work. It's tough, because you really don't want to just use their work, you want to do your own, but you also want to make the best picture/character you can. And you can do that, you can absorb the lessons without using those specific designs... but if you're not used to working in multiple styles then it will take you a longer than two weeks. So in this case I'd try to apply the lessons to new characters so that you can use them right away without being hampered by the difference between the old design and improved design.
Put them away and don't look at them. Then draw your characters again just based on the advice and tips without looking at the pics. Even if they look 'worse' they'll be yours. And I'm sure there are different ways to incorporate the tips than the way he's drawn them. I think all help is good help, even if it feels a little weird at the time.
And next time, just ask him for tips rather than a redraw. You can tell him that although you appreciate it, seeing somebody else's drawing of your character confuses you when you are trying to draw.