Firstly the speed limiter regulation changes do not cover a "P" registered vehicle, see
18-01-05 New requirements for Road Speed Limiters
With regard to the offence, if you are running on a restricted licence then it is hard for VOSA to take action against any other than the Owners/Directors, and the person committing the offence, if you have a full operators licence then the offender, CPC holder can be charged.
Any discrepancy with regard to tachographs must be recorded and some action must be taken, this doesn't include an informal chat.
If VOSA discover speeding on a Tachograph they are obliged to pass the information on to the police, however if they think it was an "out of the ordinary" offence they may not take any further action.
You must check the calibration certificate for the Tacho, and you must take some action.
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