It was never was revealed if the current 2019 version of RealBand writes out the gain-node adjustments to the .wav file with "file, save-as". If it does not ...
Here it does not, if set to Gain. (recent 2019 version)
If set to Volume it does.
Being a programmer myself I see the solution a little different.
Most people use the Merge option, since it takes many more other things into account than 'Save As'
(otherwise why have both if they do the same thing?)
If Sav As Wav is invoked, have the app then check for Gain Nodes .. and if they exist, offer an option to treat the Gain Nodes as Volume Nodes so they get incorporated in the wav. Then have it do the math on the Nodes (CC change number and value adjustment) then go ahead and save it.