If you chose the "Radio Object Swap" option when installing the mod,  you will have a file named "WRAR3_SWAP.ini" in your data folder. You can open that in MO2 or any text editor and you will see these lines:

[Forms]
;RadioDiamondCityReceiver
RadioDiamondCityReceiver|WRARReceiverOn|NONE|chanceR(25)
;RadioDiamondCityReceiverOff
RadioDiamondCityReceiverOff|WRARReceiverOff|NONE|chanceR(25)

All you have to do is change the "25"s to whatever percentage you prefer. For example, if you'd like it to be 75 percent, you would change it like this:

RadioDiamondCityReceiver|WRARReceiverOn|NONE|chanceR(75)
RadioDiamondCityReceiverOff|WRARReceiverOff|NONE|chanceR(75)

This would result in any instance of the Diamond City Radio object spawning in your game to have a 75% of spawning a WRAR radio, instead.

Save the file and game on.

I suspect that these swaps only occur the first time you enter a cell, so keep that in mind.