I've been thinking over this one for a while now, then once on here forget about it! Until now

I'm wondering if an alternator can be modified to up its maximum output or do I have to buy one that's already built from the factory to a higher rating?
I'm asking this as I'm running so many accessories these days that even just cruising at night with the EJ engine management gear, factory high beams and three 130W driving lights has the battery's voltage sitting on about 12.4/12.8V Add the thermo fans and I drop another .2V
I don't know what it runs when I have the Engel and cooler all running at the same time as I've not tried that yet with the new volt metre I've got.
So I'm wanting to upgrade my alternator to something with a higher output. Has anyone got any ideas? I've heard of the H6 alternator being 100amp but I don't know if I would be able to get the matching plug so I can wire it into Ruby Scoo, plus I can't afford a new H6 alternator!
I've got no room for a second alternator either, plus I don't know how to wire this in with the original alternator.
Any info is much appreciated!
Cheers
Bennie