FWIW, you shouldn't interpret all this rambling as the answer to your inquiry. Most of this thread has no correlation to your issues.
Have you tried this method?
SetEnvIf Referer ^http://www.example.com keep_out
My htacess is very, very large, while utilizing refers, UA blocks, and a multiple of other methods, which all function fine and as intended.
My ErrorDocuments also function, however their configuration must be defined in CP.
I did not copy and paste the complete instructions, which also sstates to include in htaccess.
BTW, I pay less per month than you, in fact, I pay one-fourth of what I paid for 8-9 years and for that same price get multiple domains hosted.
The inconvenience of the ErrorDoc's is trivial. My host provides excellent support and has worked with me on some key issues.