When you first add a cylinder, you have the option to change the number of vertices, etc, but once you do anything else in blender, it seems you no longer can edit those parameters.
Is there a setting anywhere or an add-on that allows these parameters to be edited later on? If not, how easy would such an addon/feature be to create for anyone reading this?
Blender does not have a construction history. You can only edit the parameters of the last action, nothing earlier than that. To edit the parameters of the last action you can use F6 or the Operator Tab in the Tool PanelT
If you want to modify the last tool you have to do it before using another tool.
There is a workflow solution to this. While you're making a model, if you think that you may want to change one or more parts of the model, make that set of parts separate bits of the mesh. This can be achieved with a vertex group, or just by leaving the part of the mesh unconnected to the rest of the object.
When you decide to select on part, select it by using the defined vertex group, or if you've left it unconnected to the rest of the mesh, by selecting a point on the part and pressing CTRL - L, or by pressing CTRL [numpad] + until the part is selected. Get the necessary parameters of the part (especially the median point location), or create the new one, if not at the desired location, in a way that you can move it there, and when it is in the desired place delete the original.
With Blender 2.8 at least, you can always hit the F9 key and you´ll see the operator panel again.
