BuddyPress.org

So, you want to change the 358?
you can do that with something like this

function cc_custom_excerpt_length() {
return '20';
}
add_filter( 'bp_activity_excerpt_length', 'cc_custom_excerpt_length' );

Using that will change the activity excerpt length to 20.

Disclaimer: i am not a professional and this is not advice.

This line’s controlling it.
$ending = apply_filters( 'bp_excerpt_append_text', $ending );

So, we want to use

function cc_excerpt_append_text() {
return 'Stop Reading';
}
add_filter( 'bp_excerpt_append_text', 'cc_excerpt_append_text' );

Again, just change ‘Stop Reading’ to whatever you want to replace it.