Only thing that changes draw length on a bow is twisting strings and or adjusting or changing cams. Tieing a string loop on the string only changes your anchor hand position by the length of the loop.
Mine is set at 29 inch draw.
I can take off the loop and it will still be 29 inch draw.
I can add a 3inch loop and it will still be a 29 inch draw but my anchor hand would now be three inches behind my head. Understand??
String loops do not change draw lengths. never have and never will...

I think I' ve beat this dead horse enough.

Good luck....