With Vam 1.20 you couldn't but now, with 1.21 you can. Using the new "overlay presets" feature.
Normally, presets save every aspect of the model they're made for. And when you load them, the current features are replaced by those in the preset.
But with overlay presets, you now have the option just to save (and load) certain aspects of the model, and leave the rest unchanged. In this case, you want an appearance preset overlay that adds a couple of morphs and a clothing item.
To make your preset, select a model, go to "appearance presets" and press "load defaults. This loads the default base model. Remove all the clothing.
Now apply the clothing item your talking about and apply the morphs you want associated with it. No other morphs, clothing, hairstyles, textures, or anything.
Now go to "appearance presets", enter a name as usual, but instead of pressing "Create new preset", press "create new overlay preset". This saves the preset containing ONLY those items that are not part of the default model.
Your done. Whenever applied, that preset will add the clothing item and morphs on top of the existing model without changing anything else.
When saving an overlay preset, Vam lets you enter any name you like. But personally, I think it's very useful to be able to tell normal presets and overlay presets apart when I see them in my preset menu. So I'm using the convention of starting overlay preset names with "!". Like "!somePreset". This also has the advantage that if you sort presets alphabetically, it will list all the overlay presets first.