why did you need to work on the transformer ?

if you only wanted longer wires then I would of spliced extension wiring to the transformer

if you removed some turns from a winding to lower the output voltage
then I would replace the original tape with new heat resistant tape
eg
glass cloth electrical tape with thermosetting poly acrylate adhesive/ heat class F

Any 3D printed support needs to withstand the temperature the transformer runs at

your probably looking at a 3D plastic part that needs to be safe at 130 to 150 C
and not prevent the natural cooling of the transformer

John