There is a bunch of techniques to prioritize your backlog.
Scoring models (value vs effort, value vs complexity, RICE etc), KANO, MoSCoW, adoption of Delphi method (Buy a feature, Cost of delay), yadayadayada.
The successful application of prioritization framework depends from your situation. If you have a dedicated person who can justify all business needs, you should have no any issues. Just give this person title "Product Owner" and explain him Business Value concept.
Your team have pipeline about 100 change requests per year (2-3 per week), most probably you operates with bunch of different stakeholders (hopefully whey are not conflicting). The real challenge is how to align such amount of people around the similar priorities understanding. In my practice in such situations the "Cost of delay" method was most successful. This concept is pretty clear for most of the business people since it's explains everything on their native language.
For reference you may check how WSJF matrixes in SAFe have been designed, it's very practical.
Here is good read about existing techniques.
And, btw, congratulations.
If someone send you 2-3 change requests per week, it means the business people is really interested in your job :)