Another thing is that regulations don't only consider radiated power. Constant-level spurious transmissions are sometimes tolerated to a higher degree compared to modulated ones (e.g. in some bands maximum allowed interference is determined by quasy-peak level, not power). This is exactly because modulated interference (which is what this produces) is more harmful to communications systems.
Take powerline ethernet where the power levels are "low" but still can cause significant issues[2].
[1] http://www.arrl.org/part-15-radio-frequency-devices#Myths
[2] http://www.elmac.co.uk/RF_Emissions_of_Powerline_Ethernet_ad...
Low risk overall but it's a good reminder.
It's very possible to transmit illegal power levels with software mods, or even carefully crafted data packets in some cases.
Unless you’ve made custom PHY hardware for those data packets to be pushed onto the line through, your data packets are going to be line-coded to ensure that the signal is self-clocking. Which basically precludes boosted harmonics.