I have a script, and I want to add some values to my data in a specific row and column. There are no unique values to where I could use an if statement to signify the row. Are there any other options to do this?

[#1]

Here are a variety of ways to directly access specific row/columns and change their values.  They are all documented in the Scripting Guide.

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names default to here(1);

dt=open("$SAMPLE_DATA/big class.jmp");

:height[2] = 99;

dt[4,4]=88;

column(dt, "Height")[6] = 44;

:height[dt<<get rows where(:age == 13)] = 21;

:height[16::20] = 34;