BuddyPress.org

Well these are common WP type functions – have a look at the codex.
https://codex.wordpress.org/Function_Reference/add_filter

If you’re building a site – might as well try changing it the correct way instead of informing others to hack the bp-core. (as that will just lead to bigger problems down the road for those who may not understand the changes made). BuddyPress is littered with hooks

something like:

function my_blank_activity_permalink( $content ) {
return ”;
}
add_filter(‘bp_activity_permalink’, ‘my_blank_activity_permalink’, 1, 1 );