Index unusable rebuild

I have several jobs which create some read-only tables:

drop table t1;
create table t1 NOLOGGING pctfree 0 as select...; create index i1 NOLOGGING pctfree 0...;

I would like to truncate the tables and indexes rather than drop them (I would like to be able to make persistent changes to storage parameters). I would like these operations to be performed with nologging. I have tried:

truncate table t1;
alter index i1 unusable;
insert /*+APPEND */ into t1 NOLOGGING select...; alter index i1 rebuild NOLOGGING;

However, I am getting (something like) the following error:

ERROR at line 1:
ORA-26028: index I1 initially in unusable state

How can I instruct Oracle to ignore an existing index during a direct-path insert? How can I establish a NOLOGGING operation for both the table and index rebuild?

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