There’s anyway to apply snapshots on event buses, instead of group or return buses?
No, it is not possible.
The reason for this is that input buses (also known as ‘event buses’) were deprecated in FMOD Studio version 1.07.00. Since only buses can be scoped into snapshots, the deprecation of input buses meant that it was no longer possible to scope them into snapshots.
If you want to use snapshots to affect specific events, simply create a group bus for each specific event, route the events into their respective group buses, and scope the group buses into your snapshots.
The deprecation of input buses was previously mentioned here: http://www.fmod.org/questions/question/unable-to-see-input-track-in-mixer-window/