Yes. One objective but multiple decision variables. You need to find a way to combine those variables into expressions that connect them. Maybe you can compartmentalize the problem into sub problems — optimize locally and then aggregate into a global optimum?
Not sure if what you're saying is the same thing I did today but my boss discussed having the same draw each month or changing quarterly. I played around with solver for the same each month and for stable changes (amount halves every year or amount goes down X% each month). So that way I can set one objective and have that positive or negative growth reference it. It worked well except it was more money than I hoped. What I realized though was that the credit we're drawing was already more than the 1.25 mil I wanted to stay under. I may have to play around with assumptions to make it work.
The thing I don't like about solver though is that it's not dynamic.