Maybe I don't fully understand, but why not use the default checkboxes for modifier keys? (Requires 4.020 alpha) The general idea for the "generic device support" is to just provide the triggers of a device and then use BTT default UI to configure them (although your approach should also work).
yep i did it already. but its not working %100 of time. tested on latest alpha
on the first half of video i only sended normal thumb, and you can see its scrolling up same time
scrolling distance its same as page up (or fn+up). its not an arrow up event
on the other half of video i only send opt+thumb but its not fully successfull. it shows desktop %50 of time
fyi i tried to check which key codes sending with keycaster app. it started open app expose instead of mission control. i guess other monitoring apps not friendly
also im using linear mouse it only captures back-forward buttons and mouse movement. it didn't change result when i closed it.
i tried block scrolling action, it solved scrolling but it shows to action selection menu
i guess this one related with disabled triggers not really disabled. it shows context menu even if i disable both events. but it still shows context menu if i remove trigger with OPT
i guess it not solved scrolling event, it just send to context menu