No it won't as you didn't include the lower case "s" among the delimiters of the Part() calls within the Begins(). But the bigger issue is that you will always be debugging and wrestling with the limitations of the formula language. In JavaScript you can parse any pattern whatsoever using regular expressions and compute any output you desire - effortlessly. One short regular expression /S5\d{3}/g will parse out all the S5* tokens:
var f = "I HAVE SASSAFRAS AND BOXES OF S5442, S5443, S5444, S5445, S5446, S5447, S5448, S5449, S5450, S5451, S5452";
f.match(/S5\d{3}/g).join("\n");
result:
"S5442
S5443
S5444
S5445
S5446
S5447
S5448
S5449
S5450
S5451
S5452"
