If I understand your question, then the answer is likely to be, "yes." Any field that is in the view can be included in a reference line label. If the field is not already in the view, just place it on the detail shelf.
If you can post a sample packaged workbook illustrating what you want, we can likely help. See Posting a Perfect Question, Getting the Most From the Tableau Forums and Anonymize your Tableau Package Data for Sharing for more information.
Thanks for your input However, my question is asking "How" not "If"...
I want the reference line to be placed at One Standard deviation away from the mean (which displays the SD value rather than Mean +/- SD)!
Would like to know how this can be done and if it is possible.
I already described how to make the label be different than the value, which is what your question appears to be. If that is not what you want, you will need to be clearer and, once again, if you can post a sample packaged workbook illustrating what you want, we can likely help. See Posting a Perfect Question, Getting the Most From the Tableau Forums and Anonymize your Tableau Package Data for Sharing for more information.
Digging this up again...
After searching around for a while, I haven't found an answer to Sidra's original question.
I have a simple bar chart with current MTD sales, a reference line with the current month's quota, and a reference line showing the current percent through the month (based on percent of workdays through the month * current month quota).
I'm looking to label this second line with the percentage rather than the calculated amount. The pill is on the detail shelf, but I've found no way to include it in the custom label field of the Edit Reference Line dialog. I had hoped using the same syntax as labels or tooltips would work -- in this case <MAX([InvoiceDatePercentMonthWorkdays])> -- but sadly it did not.