Thanks for your email.
I would say that when applying to a front office role the fact that you have previous banking experience, regardless of what role would be a positive. I don't believe that it would tarnish your application, however I would clearly demonstrate why/what skills etc you have that make you a more suitable fit for the front office, and I would recommend that you leverage off the experience and knowledge you have and sell yourself in that way. This of course is a personal view and so can't assure you that everyone thinks this way, however I would think that this would be a common answer.
Hope this helps