I'm not sure to have understood your question: do you want to have an icon instead value not for all rows but only for one?
I'm not sure that it's possible, you can substitute all the values of a column with different icons based on range values.
I suggest to download Splunk Dashboard Examples 6.0 App (https://splunkbase.splunk.com/app/1603/), there is an example (Table Icon Set (Rangemap)) for your need.
Every way to change values of a column with icons you have to use rengemap command (
| rangemap field=Total severe=0-0 low=1-1000000000 default=severe) and add two files to you App:
the content of value1 to valueN shouldn't change this is my problem and don't forget i have a search with a command |transpose
also the rangemap accept numeric value for range, and the content of value3 is alphabetic.