If it's just inventory management for cop cars does this mean you're just tracking make, model etc for each vehicle?

This sounds like a great way to learn what is useful about such a thing for the cops and then subtly disrupt it in favor of the people. I recommend taking the job and giving yourself a learning phase where you get a handle on what is what and how this information is actually used.

For example, if it really is about fleet management then it's probably about oil changes and that kind of crap. Tracking this info is mostly about saving money for the city and so they might quickly trace problems back to you so this is more subtle than simply helping cops or throwing a wrench in their operations by doing a bad job. You'l want to ask tactical questions. What happens if a specofic kind of info is missing? Late? Wrong? What if it is tracked better, with a high degree of fidelity and timeliness? Is anything hidden from budgeting? The public? Could it be revealed?

I would bet that most info is relatively neutral or will take serious thinking to evaluate. Let's say you find a way to make life more expensive for the police department. What happens next? Well, this depends on your city council. Will they simply increase the police budget? If someone removes the wrench you threw in, will the cops' budget decrease or will you have effectively just helped increase the police budget that they can use for buying tactical gear and covering up their crimes?

The power to overtly and coherently fight the police lies in political organization. In preventing city council from increasing the police budget. If you make the PD more expensive at the same time that city council refuses to increase its budget, you will have done good work. If you do this when they will increase its budget, you might have just de facto defunded a good program, as city councils will usually shift money around to fund cops.

So I recommend learning as much as you can and being strategic. You are probably not helping cops very much in the first place but as you understand the role better you might be able to hurt them in the right way at the right time, messing with their budget. You'll also get a lens into how the city really operates and can do that salting work that is probably far more impactful. It is a more strategic path to hurt police budgets by having a powerful union to advocate against cuts to any other department. And to do things like kick cop unions out of union coalitions.