a while ago i talked about how i felt that trans people needed to provide a ritual for cis people to engage with to help them understand the change of boundary of transition, and to allow space for them to express the common conflicting feelings that arise when you realise that someone you have known all their life turns out to be not be exactly that person an action to grieve but also an action that turns that energy into celebration for the new.
Turns out the Humanist organisations do actually offer renaming ceremonies that may be able to function in exactly that manner. Humanists UK at the very least have mention on their site that their celebrants are open to hosting a ceremony that would be a renaming in the case of a trans person.