No; in the US, for example, Part 15 devices are, I think, limited to a maximum of 1W transmitted power at 2.4GHz, and 4W of EIRP (effective isotropic radiated power). i.e. maximum antenna gain of 6dBi at full power.

For fixed, point-to-point installations there is a special rule in effect: you can get more EIRP by having higher gain antennas as long as you back off the power; e.g. you can drop down to 22dBm (159mW) but have a 30dBi antenna and get 52dBm (159W) of EIRP.

A 30dBi antenna at 2.4GHz is, by the way, something like a 1.5 meter diameter parabolic grid.

> Could I emit 500W or more with whatever modulation or lack thereof and not be prosecuted

You could emit 500w in the 2.4GHz ISM band legally as a ham radio operator, as there is an overlapping ham allocation, so long as you complied with the ham requirements (which limits you somewhat on the 'whatever modulation' front).

But why would you? You're limited to line of sight communications -- far less than 500w will get you to the horizon. :P The only application I can think of for 500w at 2.4GHz would be moon-bounce. :)

Outside of the ham radio overlap, any intentional transmission in that band would have to be via a type-certified device. ... So it's more a question of what devices the fcc will certify than what you're able to do.

2.4GHz is unlicensed, but through a few different routes FCC regulations prohibit operating, distributing, marketing, etc an intentional radiator (and many types of unintentional/incidental radiators) without an equipment authorization or device certification. So the pedantic answer is that you can do whatever you want in 2.4GHz but you can't do it using whatever device you want, which creates limitations of generally 1W as sort of the simplest answer.

"Unlicensed" does not mean "Unregulated". There are still type-approval requirements for almost all transmitters (except Amateur radio where the responsibility falls on the licensed operator, rather than the actual equipment).