No, once a job has been submitted the JobOwner attribute cannot be changed. The JobOwner is marked as an IMMUTABLE attribute, and so the Schedd will not let you change it. The JobOwner is the Unix/Windows identity of the job, and it would be a security violation for it to change, and because of this the Schedd keeps some internal data structures about the jobs owned by a specific uuser and will not update those data structures except when jobs are created and destroyed.
This is not an issue specific to the Python binding, the JobOwner cannot be changed by any tool, and will not be changed by the Schedd itself.
You will have to remove the job, and submit a new job with a new owner.
You can, however, change the AccountingGroup attribute of the job, which will be used by the HTCondor negotiator and by the Accountant If it exists.
It is possible to change the job ownership in Python binding?