I'd like to double the number of games of my SuperBlitz 73 engines from 72 to 144, playing for each couple a second game with reverse colors. After having done a backup of the current tournament pressing "New Tournament" (all OK in Recent tournaments) then I have reloaded it, exited BSG to avoid possible locked files and finally edited Banksiaplaying.json changing "games per pair": from 1 to 2. Nothing happened once I have reopened BSG
Add new games trick seems to work, I must only check if games are played with reverse color, but maybe you can modify the existing script to do that
(Experimenting the trick adding new engines and clicking 2 times instead of replacing them so I can simply remove them from crosstable if there are errors )