radioChannelSetCallSign and radioChannelSetLabel are set commands with no get variant.

Would work like this:

my_channel = radioChannelCreate [[0.96, 0.34, 0.13, 0.8], "Q-dance Radio", "%UNIT_NAME", [player]];

my_channel radioChannelSetLabel "test_label";
my_channel radioChannelSetCallSign "%UNIT_ID";

radioChannelGetLabel my_channel
-> "test_label"

radioChannelGetCallSign my_channel
-> "%UNIT_ID"