But every time I run the FSDT Universal Installer's 'Config' (which is necessary after adding new liveries), it automatically changes the entry back to "false" in some but not all model.cfg files. Weird!
The FSDT Installer doesn't do that, since it doesn't touch that line.
However, when it adds a new livery folder locally, it *copies* the entire model.cfg of the original airplane so, instead of repeating the change in all added liveries, you apply the change to the original model.cfg, it will be copied as such when reconfiguring new liveries.