You can refer to HEI Standard for Air Cooled Condenser for some general info, but you should have performance curve(s) from the OEM which would indicate your design limits. Yes, an increase in steam flow (above the design steam flow) to the ACC would impact the ACC performance because the overall heat input has increased and if you cannot increase your cooling air speed any further than you would have a decrease in performance, likely shown as increased turbine backpressure. Usually, the ACC would be designed for a baseload or max load case steam flow conditions coincident with a site summer design ambient air temperature case. That would size the overall surface area and air speed (i.e. fan & motor sizing). Then your main variable for a performance curve is ambient air temperatures and/or reduced cycle steam flow cases. If your ACC was undersized then you could investigate increasing your fan blade pitch to increase air flow, but the motor load would need to be checked to know how much margin you have. You also need to be wary of freezing concerns in winter operation, depending on your site location.
Recently we contracted EVAPCO to perform an assessment of our ACC including cleanliness of fins, thermal imaging, air flow measurements, and operational data analysis to determine ACC performance and available capacities. They did a pretty good job.