Some of the chargers accomplish support for things like the iPad 2 by shorting the two USB connectors. Some advertise things like 2000ma, but fail to deliver much more than 500ma. I am not sure if this is due to the choice of shorting out the data connectors to trick your phone in to thinking it is plugged in to the wall.
Back in the WM 6.5 days, you could accomplish this at the phone driver level and did not need to modify your chargers.
I would not worry about trying something rated higher as your phone would regulate the current. I personally intend to do my experimentation by shorting out the cable rather than the charger (cables are more easily replaced). Unfortunately, there is no app for WP7 that can measure the charging current, so the only way to do this scientifically is to use the battery status app and measuring the charge rate over time.
If you do the mod, post back and let us know. When I get around to the USB cable experiment, I will post back as well.
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