It sounds like you mean animated patterns. There isn't a built-in tool for modifying patterns, but Decker includes scripting APIs that could be used to build one. For example, the PatEdit contraption can edit patterns themselves, and the AnimEdit contraption can be used to configure animated sequences (patterns 28-31) of the static patterns (2-27). You could also set up animated patterns manually with The Listener.
If you actually mean brushes, the decker reference manual section "Brushes" describes how you can define your own. Decker comes with an example deck that contains several custom brushes.