As a general note, the example of the oil rig race brings up an important point. NOTHING said at a skippers meeting is official, unless it's in writing (in the NOR, SIs or a WRITTEN amendment).
There are some times when it is desirable to allow changes to be made verbally, but the procedure for this must also be, you guessed it, in writing.
Mike is absolutely correct. Oral changes to the sailing instructions can be made only on the water, and only if the procedure is described in the written sailing instructions. Changes may not be made orally at the competitors' meeting. In fact, there is no requirement to attend a competitors' meeting at all.
Regards,
Eric
