I have a bad upward curve from peyronie's disease
which DLD thinks is awesome. I was going to try
and jelq it straight again but DLD said that it took
him years to jelq his upward curve.
So I would say that you could jelq a curve or even
jelq a curve straight again. An upward curve I guess
is desirable and women love it, but I don't know about
other types of curves.
Any curve can be straightened with deliberate jelqs against the curve. It is a lengthly process but it truly works. I was able to create an upward curve, as I always wanted.