This may be a dumb question... but i really haven't seen it covered here before and im curious.. This doesn't apply to my skill set as of yet.. but it definitely applies to my car in general.

how does one go about tuning an ecu far past what it was meant to rev to.

modify all the axes for higher Revs?

But becareful changing an axis might affect other maps as some axis are shared. This would then invalidate the values in the other maps and would need to be remapped to the new scale.

If you don't have a complete map pack you may of course not see these maps at all.

The ecu should be fine to 10k.
At least the old ones are designed with 10000 rpm in mind, I can't imagine that they took ME7 a step backwards for some reason.
Theoretically the parameter re-calculation speed suffers somewhat as the CPU spends more time handling real-time interrupts, but I doubt you will notice.

As for raising the rev limit without changing anything - the last value from the map will be used.
So if your map's RPM axis ends at 6500 then every RPM higher than 6500 will use that value.

It's the same for everything else as well.