Yes you can rewind a primary to 230V used in Euro zone if the core is uncapsulated or even the secondary, I have not located the detail you mentioned sorry, it a big PDF.
OBS.: Ok just found it with another browser, This schematic transformer show two primary 117V each to be used with bi-phase 117V + 117V mains outputing 234V at secondary.
It dont grant your amp was assembled this way it must be checked in loco and tested. You must have 4 wires at the input transformer Brown, White, Black, Blue.