Is it possible to loop and merge based on a free text response?

I'm drafting a survey to send to managers at a company that will ask each manger to fill in data about only the employees who directly report to them. I'm currently using a matrix question (with each row representing a direct report) that loops and merges based on who the manager is. I used the guidance supplied in this forum: https://www.qualtrics.com/community/discussion/comment/12807#Comment_12807 The loop and merge is currently based on the answer selected in the manager drop-down question (e.g., question = "Which manager are you?"; answer choices = "Manager A", "Manager B", etc.). However, I don't want to allow Manager B to intentionally or accidentally select "Manager A" and then be able to see Manager A's direct reports. Ideally, each manager would start by only seeing their direct reports (if I could somehow connect the loop and merge to the unique survey URL attached to each respondent). If that's not possible, another idea is to email each manager with a hard to guess passcode (e.g., "X2Q73CH"), which they'll type in and the loop and merge will be based on their free text response. However, I'm only seeing loop & merge options for numbers (1 through X) and drop-down lists. Is there a way to base a loop and merge on a free text response (assuming I'd enter each of the unique passcodes into Field 1 in the loop & merge table)? For context, I'll be reaching out to ~200 managers - each will have a handful of direct reports (none with >10 reports) to answer Qs about. Thank you in advance!