Testing on Logical Standby Database
My procedures seem valid... I was able to test the logical DB, then bring it back into an exact copy Logical Standby and re-enable SQL Apply without issues.  

However, there was a minor change to my procedures: flashback database requires that the DB is in mount state and that alter database open requires resetlogs or noresetlogs.

Therefore, the amended procedures are as follows:

PRIMARY
alter system set log_archive_dest_state_3=defer scope=both;

STANDBY
alter database stop logical standby apply;
alter database guard none;
alter database flashback on;
create restore point before_testing guarantee flashback database;

*AFTER TESTING IS DONE*

STANDBY
shutdown immediate;
startup mount;
flashback database to restore point 'before_testing';
alter database open resetlogs;
alter database guard all;
alter database start logical standby apply immediate;
drop restore point before_testing;
alter database flashback off;

PRIMARY
alter system set log_archive_dest_state_3=enable scope=both;