// Works & effectively sets the value for custcol_fname to TEST 1 for line 1
var nsRecord1 = nlapiLoadRecord('customtransaction_anon', 8221);
nsRecord1.setLineItemValue('line', 'custcol_fname', 1, 'TEST 1');
nlapiSubmitRecord(nsRecord1);

// Code gets executed successfully but the value for column field remains unchanged
require(['N/record']);
var RECORD = require('N/record');

var nsRecord = RECORD.load({
	type: 'customtransaction_anon',
    id: 8221
 });

nsRecord.setSublistValue({
	sublistId: 'line',
	fieldId: 'custcol_fname',
	line: 0,
	value: 'TEST 1'
});

nsRecord.save();