There is already an implementation for snapshot select override (predicates). Oracle's predicate can be improved further by specifying "AS OF SCN" predicate.
This issue is created to address that.
Given below predicate:
snapshot.predicate[SRV_EVENT = WHERE applied_to_class = 'UNIT'
This can be appended with placeholder %scn% to create the resulting predicate for oracle:
snapshot.predicate[SRV_EVENT = #scn# WHERE applied_to_class = 'UNIT'
#scn# will then be replaced with "AS OF SCN XXXXXXXX", where XXXXXXXX is the SCN number.