Switching between cw and modulated data

Hello all,

I am working on my first GNU Radio project. This will become a test
transmitter for a receiver we use at work.

The transmission scheme calls for a few seconds of unmodulated carrier,
followed by manchester-encoded and phase modulated data, terminated by
another second of cw. The cw should correspond to a modulation of zero
degrees.

What is the proper way to implement this? Initially I had planned to
implement some kind of logic outside of the flow graph, but I don’t see
this working reliably in terms of timing. Should I reserve one value in
the stream for zero degrees modulation and somehow bypass the manchester
coder for this?

Any hints would be much appreciated.

Many thanks,
Martin