You could duplicate your list, fill it with test data, then see what happens to the test the change to your custom field.
How to duplicate list:
1) Go to Site Contents
2) Go to + New > List

3) Choose From existing list

4) Choose the list from your team (this site) and press Next > Give the list a name and press Create
5) (if you want your exact data from the other list) Go to your list with data > Export to CSV

6) Open up the CSV
7) Choose the data from the list (you may have more columns) and copy it (CTRL+C)

8) Go the the new list > Edit in grid view

7) Press to the left of the first cell (you can hit the plus sign) > Press paste (CTRL+V)


You will now have your other data set to work with. You are now free to test if this will work with your custom field .
If this is helpful please accept answer.