Hello! I have a question - is it possible to corrupt Sydney while remaining an Angel TF?
Unless something changes in the future, the act of holding hands is not going to cause you to straight-up lose your Angel TF (nor for that matter will kissing or losing oral virginity), unless you are only in the early stages of the Angel TF. At worst, you might drop from Stage 6 (full transformation, wings) as it takes a couple days to recover the purity loss while you regen to max purity, but you can recover the full transformation as long as you have the Virgin trait. In fact, assuming you are at a high "angelicness" you probably could tough it out without even noticing a difference unless you somehow are making use of Banish on a regular basis.
However AFAIK you will end up hitting Fallen status going through the entirety of Sydney's corruption route (there may be an exception for girl/girl, but I'm not certain about that one). Short-term, though, you can hold someone's hand without entirely losing Angel or going into Fallen status.