Right now it is impossible by the design of feature. UDA's are
just bits of information attached to symbols. They don't affect
type of symbol and their own type is affected by symbol either.
Such enhancement is theoretically possible but that would have
been a very big change.
Current idiomatic way to do such stuff is to have single mixin
statement that iterates over all symbols of a module and does
something for those that have specific UDA attached:
@token!42
void foo() {}
mixin registerAllTokens!modname;