I would like to switch the output of a Node from a standard function to a nengo.process programmatically.

In practice, I would like to achieve this:

```
input_node = nengo.Node(
output=lambda t: np.sin(t) if t < learn_time else nengo.processes.WhiteSignal(60),
size_out=dimensions
)
```

but I am getting the following error when the switch occurs:

`nengo.exceptions.SimulationError: Function '<lambda>' returned a value WhiteSignal(period=60, high=5, rms=0.5) of invalid type <class 'nengo.processes.WhiteSignal'>`

Is there no way to return a `nengo.process`

object so that it works normally as:

```
input_node = nengo.Node(
output=nengo.processes.WhiteSignal(60),
size_out=dimensions
)
```

I guess I could always save the weights from the Connection I’m interested in and re-run the simulation with a new input node, but that would be a much bigger hassle.

Thanks for any help you’ll be able to give me!