another possible BASH way - create a helper function which processes the stdin with `read` command and then prints extra line(s):

 $ function append_lines(){ local data; while read -r data; do echo -en "$data"; done; echo "$*"; }
 $ echo "[`date `]" | append_lines " +suffice_;line1" " ++line2" " +++line_3"
 [Mon Aug 21 16:00:37 CEST 2023][ +suffice_;line1 ++line2 +++line_3]

where 
- `while read -r data; do echo -en "$data"; done;` - just passes the stdin (pipe) through
- `echo "$*";` - prints all arguments of append_lines() to stdout