How to change job code for employee keeping the same position name?

We have realised that job codes assigned to some of our employees are incorrect. As the job code at the employee record is taken from the position the job code will need to be updated at the position first. However as per the user guide once the job is assigned to the Position it cannot be updated. Please help, this is a really urgent issue.

Example

Current situation:

Employee name - John Cooper

Position - UK_BEL_HO_Finance_0114|Process Manager

Job - Manager

What we want is:

Employee name - John Cooper

Position - UK_BEL_HO_Finance_0114|Process Manager