Originally Posted by Pleiades

Theoretically you can change the stator windings on an alternator to produce a higher peak output, but in most cases this will adversely affect the low rpm output of the alternator. If you go too far searching for higher peak outputs, you can actually end up with a discharge at idle and low speeds. In order to increase output across the entire range of speeds, the alternator needs significant modification to stator and rotor.

The simple way to achieve a higher output is to put fewer windings of a heavier gauge wire on the stator, which reduces the impedance and allows more current flow. Even that only works if the is enough magnetic flux to excite the windings. More windings of thinner gauge wire make more efficient use of lower magnetic flux and give better performance at low rpm, but give a lower overall output. It’s not easy balancing the two.

It’s not just the stator than needs modifying. The size of the rotor’s iron core together with its field windings is another problem, and you can’t easily change that on a motorcycle alternator. Not enough core/windings here and then it will saturate, won’t generate enough magnetic flux and limit the peak output than can be achieved.

Another problem is that the rectifier diodes will get hotter with any increase in current flow, even if it is within the 35A limit of the (not brilliant) Tenere unit. That additional heat will need dissipating somehow, either by fitting a bigger heatsink and or relocation of the reg/rec unit. Alternatively source a higher spec reg/rec unit.

You may be better, fitting a split-charge system and another battery to power the extra accessories that are taking you above and beyond the charging system’s capacity. (Good luck finding the space, although at least you can get dry batteries now that can be mounted side-ways and up-side-down). A dual battery system isn’t going to give you more power necessarily, but what it will do is ensure the bikes essential circuits for running will always have power and you won’t get caught out. Split charging also means you don’t need to upgrade any wiring, you just fit a new loom to supply the extra equipment from the second deep-cycle battery, rather than having to beef up the whole bike’s wiring. Plus it'll be easier to do, can be fitted/removed just for a big trip or when needed.

All of the above is complex, adds additional weight and complexity. Are you need the extra power? Why not just work round what you've got more efficiently?