@rooots You can add the resistor anywhere you link, just put a 1kohm between the TTL (S pin) and Ground (- pin).
I prefer to put it on the laser module since that is the safest option, if the TTL wire breaks it will turn off.
You can insert it into the plug / connector and tape it, although soldering would be best.
One user soldered it to the back of his board: https://1.bp.blogspot.com/-TIc2-GChXYk/WdFrZXjgn7I/AAAAAAAAJQM/Awgx2kmt2sktcO6aihEXXYLV0bM4uT9GQCKgBGAs/s1600/IMG_20170912_194505.jpg
I'm not sure what you mean about executing multiple G-codes at one time, do you mean if you send one and then send another? That is OK, it's only when you disconnect the machine and then reconnect that the pulse happens during boot up.