Cache Busting using htaccess Rewrite rule?

This is a dead end approch as the enqueue API do not support such versioning format which means that you will have to avoid using it, which is not a great thing. Your specific problem here is that you added the rule too late, RewriteRule . /index.php [L] “transfers” handling to wordpress and nothing is going to be done after that, which means that you need to switch the order of them. And again changing the wordpress core rewrite rules is not smart, you should probably add a specific section outside of the wordpress rules section.