The TMAG5273 class includes an _i2cPort field that gets initialized by the begin() method, so it should allow you to talk to TMAG sensors on multiple I2C ports on microcontrollers that support that. But the implementation of readRegisters() and writeRegisters() explicitly use the Wire object, so they can't be used for Wire1 etc.
I tried forking the repo to fix this myself but ran into technical difficulties, not sure why.