Rewriting your job ticket

After a pleasant, slightly wandering discussion yesterday with my manager, she told that in a few months, I would have to submit to her, a rewritten job description with written/supportive documentation

and/or considering a supervisory position for 5 people. Direct reports ..all unionized.
Maybe it wasn't a good move on my part, but after I said: "Me? Rewrite my job??", I responded to the next option in a neutral, non-plussed way and said, "I'll think about it".

My position is unionized ..but it doesn't affect how much I work and my effort regardless of employer. I've also been non-unionized, management.
In short, a newly created position (according to our collective agreement) can be further refined by the incumbent after 6 months since sometimes things in a dept. evolve that the hiring manager never foresaw as a fit with job. This job is an analyst role with no direct reports. Most definitely I'm engaging in strategic planning also.

Since I don't supervise/directly manage anyone it has made it easier for me to deal with all the recent personal upheavals in life. I'm getting settled in now...but now must think of future.
Present manager is overwhelmed and needs to convert/create a position that will take upon operational management so that she can focus effort better on strategic matters. She has told everyone this. I see daily, the stresses of having 10 people report to her. This is why I tolerate, even her cussing at times.

I have been a manager before-- up to 4 direct reports. A few other jobs, there were 2-3 direct reports. I have also worked independently as sole person in dept. or part of a team.

Ever have been given the opportunity to rewrite your job/job opportunity by an employer?