The courier was BANG out of line to have altered an application, or even to have commented on it. Stakeholder management at UKBA has insisted that reports of this happening are not true because it can cause a commerical partner to be banned from future work with the UK.
If a British consulate said it was ok to work without the minimal status of a spousal probationary visa (FLR or LLR), then they were wrong. They may have been misled by the appliction the courier altered. If there's permission to work, the entry clearance will say so, or say not, whatever the case.
If you get caught, you'll be done and anything the British consulate may have said will not be taken into account unless you can produce something in writing, or it says so in your passport. Also, if you get caught and the amounts exceed a certain threshhold, money laundering kicks in because they are required to inform the FSA about it.
There are throttles at FLR, ILR, and nationality. So be careful.