Is reallocation if fixed costs across divisions unethical?

An audit might point out that the fixed costs associated exclusively with one division might be properly noted in that division's accounts.

For example, if the corporation made automobile axles and artisan bread, for example, the fixed costs associated with bread-making would require significant explanation of they appeared on the financial reports for axles. However, creative accounting can work miracles.

The crux of your question might be 'reallocation'. Your corporate ethics officer can answer your question specifically.

And often, ethics and the law are not the same.