Yes, yeast can be reused at least once if washed or reused immediately following fermentation however, for the best predictable results we recommend using new yeast each time. 

As we haven't run our own tests doing this, it would require some trial and error on your behalf. However, it should be possible to re-use your yeast from a fermentation when active dry yeast has been used.  The biggest challenge will be ensuring sufficient viability, along with cleanliness (e.g. lack of contamination), in any subsequent fermentations – to ensure best possible results it would therefore be best to use fresh sachets not far into their shelf life, however either way we cannot guarantee performance of the recovered yeast, so this will require some trial and error.