There are two ways to change the interface of a node in Houdini:
Houdini lets you create your own node types, called digital assets. The asset’s parameter interface is stored as part of the asset’s definition. To change the interface for an asset (thereby changing the interface of all nodes of that type), right click a node of the type you want to edit and choose Type Properties. See editing digital assets for more information.
You can change the interface of a single node. This change only affects that node. You can make these kinds of changes to the parameter interface of your custom assets or the "factory" nodes that are built into Houdini.
These kinds of changes are especially useful for two things:
Adding rendering properties to a node. Render properties are special parameters that give extra information to the renderer.
If you want to add parameters to a node (especially promoting parameters, such as promoting a parameter from a surface node inside an object up onto the object’s interface), but you don’t want to create and maintain an entire digital asset type for it. In other words, one-off changes.
For example, If you're making a bouncing ball animation, you might have a Transform surface node inside to do the squash-and-stretch. Rather than bouncing between the object and surface levels to animate the ball’s position and its squash-and-stretch, you could promote a "squash" parameter up to the ball’s object node so you can work on it at the object level.
See edit parameter interface for more information.
The interface for editing parameters is largely identical either way. The only difference is how you open the editing window and the scope of its effects.