Channel layout

EATRG is Elevator, Aileron, Throttle, Rudder, Gear
it specifies the order of the 1st 5 channels. It is only really relevant for protocols that have a real receiver with specified channel order (it does not necessarily correspond to the order sent by the protocol).
For the V202, I'd probably use TAERG. What you've described is TREA I think, so you'll need to map the channels (or define a new ordering which I don't recommend)

The Channel array is generally defined as being -10000 : 10000 for -100% to 100%. Values can be larger than this (generally upto 150-200%)

You should just use the same mechanism I use in the other protocols to adjust the values:just change 0x151 to the delta from 0 to 100% and 0x5d9 to the center point (value when channel is 0%)

If you choose 'EATRG' then you have defined how the Channels are ordered:
0 = elevator
1= aileron
2 = throttle
3= rudder

so you absolutely need to code the protocol mapping based on your choice of channel layout.

the definition of 'EATRG' tells the user what decisions you've made in the protocol. They can always choose to ignore it, but usually that means their model won't fly.