This is a topic that has been covered more than once on quite a few sites. However, it never hurts to review some fundamentals in Lightroom since there are new users everyday!
I received two emails last week with virtually the same question about Develop presets. Both readers were having issues when creating and applying their presets since the application of the second (or third or fourth) preset would alter a setting they did not want to alter. One reader's conclusion was that Lightroom's presets were not stackable. This, of course, is not at all true. Once you understand how presets work and how to create them properly, you can stack presets on top of one another and only change the parameters you intend to change.
The key is to be frugal in what you save in a preset.
When you decide to save your masterpiece's settings to a preset you click the + next to the word Presets in the left panel. That will bring up a dialog allowing you to configure and save your preset.
There are quite a few settings shown. You can save any or all of them by checking the box next to the setting name. In this example, we've made a change to Exposure and have checked only the exposure box. Any settings not checked will not be saved in the preset. If you open the resulting preset in a text editor you can see amidst the rest of the structural content the setting and its value.
Herein lies the key to stacking your presets. Avoid the temptation to use the Check All button saving every setting into the preset. Any value represented in a second preset will overwrite the same value applied by the first preset. For example, if I also create a preset that sets Exposure at +2 and apply it after the first preset above, Exposure will change to +2 and the previous setting will be gone.
Looking at the file in my text editor I see...
I see the same parameter, Exposure, with a different value. Lightroom can't hold two value for one parameter so the last one wins.
Now suppose I create another preset, this time changing different parameters and leaving exposure alone.
Here you see that exposure has been left where it was AND THE BOX IS UNCHECKED while brightness, clarity, and vibrance have there setting saved. Looking at the preset file we see that exposure isn't included in this preset.
So what does this tell us? If I apply Preset 3 the values for brightness, clarity, and vibrance will change in my image. If I then apply Preset 1 my exposure will change to 0 but brightness, clarity, and vibrance will remain unchanged. I have effectively stacked these two presets and changed only the parameters I intended. Were I to now apply Preset 2 then my exposure would change to +2 and brightness, clarity, and vibrance remain unchanged. Preset 1 and Preset 2 are not stackable since they both contain a setting for the same parameter.
Very often users find their presets unstackable because they press the Check All button to make sure they have captured everything. Unfortunately, if all your presets contain values for all the parameters then none of them are stackable. The better practice is to press the Check None button and then intentionally checking the boxes only for those parameters you intend to save in the preset. This will make you presets far more flexible.
Presets are a wonderful feature. And they are even more wonderful when used correctly. Happy processing!