Although there are different job evaluation systems, the outcome for each type is a grading structure based on comparing the different jobs in the organisation.
In other words, it is the jobs which are evaluated not the jobholders.
If your employer intends to re-evaluate your job because of a change in duties, the outcome may be a regrading of your job.
You should be able to participate in the evaluation process – at least indirectly. This is because well-organised job evaluation schemes should involve employee representatives. Take the time to explain to your rep or HR contact the complexities of the tasks you perform and why your job requires a multitude of skills.
Unfortunately, many people are likely to end up dissatisfied by a job evaluation scheme. If the exercise has produced an unfair appraisal of your post, lodge an appeal.