It is only possible to set a IHeaderResponseDecorator, but this replaces the current decorator. The default decorator is ResourceAggregator, which is vital to resource rendering. Also, other framework features might require other decorators. At the moment it is up to the user to set all decorators required. This is error prone, but also makes it difficult to use these decorators in framework features.
A new API is needed to add decorators without replacing them.