Hi Peter,
I don't have an answer in terms of Customization, but I'm happy to follow up with Customization experts to see what we can do for you.
Firstly, I'm wondering if you can just pull the multi-select field into a view (such as a projects view) to see if a specific value is being used? This is however limited when selecting multiple values, it uses the OR logic not AND, but it might provide an answer to your reason for testing?
Could you please clarify, are you trying to see if a multi-select field value has more than 1 value selected using customization?