If your modulation spreads the power evenly over 500kHz, if I
understand the rules right, you can transmit 1 watt. If your
modulation spreads the power evenly over 50kHz, you could transmit 0.1
watts (+20dBm). If your modulation spreads the power evenly over 5kHz,
you could transmit 0.01 watts (+10dBm). It _appears_ that you could
transmit +8dBm (6.something milliwatts) however you want in that band:
as an unmodulated carrier, or spread however you want. I don't suppose
they talk about the time period over which you measure the spectral
power density...but they probably wouldn't like it if you transmitte 1
watt that swept linearly and slowly across the 500kHz, say once a
minute. Over a long enough period, that would be uniform power per
unit bandwidth, but a one second snapshot would show 1 watt in
500kHz/60 = 8.3kHz bandwidth.

Hope that makes sense. Beyond that--see your lawyer! ;-)

Cheers,
Tom