Please help me understand unlogged tables

If a table is set to unlogged is it inherently non-durable? That, is any
crash or unsafe shutdown _must_ result in truncation upon recovery?

I can imagine a table that is bulk loaded in a warehousing scenario and
then sitting statically could be safe, but maybe the question becomes how
could the system know it is unchanged if it isn't logged...

Would a correct solution be to bulk load into an unlogged table and then
(fairly cheaply?) set the table back to being logged?

If I my mental model is correct the table would be liable to being lost to
a crash during loading but once set back to logged it is durable. Is that
correct?

Is it the case that setting a large table to logged status after loading it
unlogged is a reasonably cheap operation?

Thank you,
Alex Stoddard