Assuming that your question is 'for real' and not just to provoke a heated discussion, it cannot be answered "yes" or "no" without an in-depth, engineering structural/aerodynamic/aeroelastic analysis. I would submit that few on this forum (myself included, even with an advanced engineering degree) have the competence to do this properly; and that the degree of effort required would be more than sufficient to preclude anyone from doing this 'just for fun' and then attaching their name to the resulting conclusion.
There have been reams of words written about the implications of substituting different composite materials, altering layup schedules, etc., etc. and I'm not going to re-plough that ground other than to suggest that this is super-serious business that is far outside the realm of eye-ball engineering, 'rules-of-thumb', shortcuts, etc... And for attaching the winglets no less, arguably about the most complex and critical structural element in the entire airframe! :roll:
The super-short answer to your question is: Neither substitution (Kevlar or graphite) is acceptable because the resulting structure will have properties significantly (much?) different (maybe better, maybe worse, but for sure, different) than those intended for what is a proven design. I'll leave the long answer(s) to those who would want to delve into issues of load distribution paths in materials with dissimilar elastic modulii, the compressive performance of kevlar, graphite tensile failure modes, etc. etc.
Two alternative questions I would pose would be, "You haven't really substituted Kevlar for glass in a major structural layup already, have you?"
And, "If so, why would you do such a thing?"
