You can add presets with multiple (different) values to a single image, but you need to make sure that when the preset is saved it is only for that particular setting.
For example, if you want a preset that sets sharpening amount to 30, save that preset with only the sharpening panel settings included. Then, if you want a preset that applies a tone curve adjustment, save that preset with only the tone curve checked in in the dialog box.
In other words, if you save presets that have all the settings included, they will overwrite each other as you apply them.
Keep in mind that all the settings are absolute values. If you have a setting with a value of +7, and you change it to +10, it is not +17, it is +10.
With this in mind, you can create presets with single values to apply very specific adjustments and apply them in any sequence to a single image. Presets that do not include certain settings will not affect those settings when applying the preset.
To see this in XML, open one of the presets in a text editor. You will quickly see how the settings are actually included in the preset file.
(I hope this description makes sense, let me know if you have any other questions.)