102 = less droop
I agree with Shawn's assertion. It was explained to me that on the 139 the optimum performance is obtained from 100% Nr but during Cat A certification the test pilot must allow a two-second reaction time before intervening with the appropriate procedure (reject of Cont TO). To compensate for the additional droop caused by this 2 second wait the Nr is raised to 102%. Arguments about performance gains in this context may be interesting but not strictly relevant.
No mention of using 102% Nr in any other context than Cat A, Sling Load or Hoisting is made in the 139 RFM but I would exercise caution in using the philosophy that the absence of prohibition implies acceptability.
As always, if you wish to interpret the RFM in a particular way then you would be wise to seek a 'no objection' letter from the OEM. However you look at it, if you survive the crash and have to defend your actions in a court of law then not doing what the RFM says makes your position just a little weaker. As there is no mention of 102% Nr in any other context than those mentioned I would read it that 102% is not intended for other applications. If you disagree then by all means write to the factory and seek clarification.
G.