Why does this not work? From what I read only default values should cause issue. I'm on release 9.4.4:
bms=# ALTER TABLE trap ALTER COLUMN trap_timestamp TYPE TIMESTAMP WITH TIME ZONE; ERROR: ALTER TABLE ... ALTER COLUMN TYPE may only affect UNLOGGED or TEMPORARY tables when BDR is active; trap is a regular table
Generally ALTER TABLE commands are allowed. There are a however several sub-commands that are not supported, mainly those that perform a full-table re-write.
...
ALTER COLUMN ... TYPE - changing a column's type is not supported. Chaning a column in a way that doesn't require table rewrites may be suppported at some point.