I am modeling a tank with RISA. I am using the special shapes assist. I need to modify my input on the hydrostatic tank loading. Is there any way to do that other than to create a new model?
I take it you mean that used the "high level generation" or "Insert-Structure" utility to create a "Cylinder with plates and stiffeners".
If so, this is a one time action. It generates a structure with the geometry and load specified in the interface. If you need to modify that load later, you may modify it manually. But, with hydrostatic loads it is tricky because they are a series of plate surface loads, not a single load. If all you want to do is scale the magnitude up or down, then you should be able to do that easily enough in the spreadsheet. But, if you which to change the height / depth of the fluid, then I cannot think of an quick or easy way to do this.
I would say re-generating the tank with the correct liquid depths could be your best option. Rectangular tanks are a good bit easier because you can use the "wall panel" feature to create the walls, and the loading for wall panels is a decent bit easier.