The mod is available as an option; I think it's mod. no. 072157. It involves a few hardware changes [torque gauge, limit light logic, and I think collective anticipator]. The end result is that the MAUM is increased to 2600kg; helipad weight at ISA is 2550kg. There is no increase in the power limits though so for prolonged hovering it has only a slight advantage. For the corporate user however it's quite handy. No idea what the mod costs.
I also seem to recall that the French military have operated their 555Ns at 2700kg but that they -spookily- got through quite a few main transmissions.
email me if you want to discuss "N" stuff in detail.