Formula Column are very restrictive.
If the entries of a JMP column are defined by a column formula , there is no possibility to change individual entries, neither manually nor via JSL:
dt = Open( "$SAMPLE_DATA/Big Class.jmp" );
dt << new column("row", Formula(row())) << run formulas;
:row << suppress eval;
Try(:row[5]=7, Caption("change a cell of a formula column via JSL? doesn't work"));
Wait(2);
Caption("try to change a value manually ...");
Python send(dt);

Actually, there is a backdoor: Python
Python send(dt);
Python Submit("dt['row'] = [1]*40")