I will echo the other answers that suggest a merge is the best way to do this.
But if you absolutely must code the lines item-wise (again, messy) you can generate a long list ("pages") of replace commands by using MS Excel to "help" you write the code. Here is a picture of your Excel sheet with one example, showing the MS Excel formula:
columns:
A B C D
row: 1 last first id code
2 MARTIN JACK 103 ="replace fname=^"&B2&"^ if id=="&C2
You type that in, make sure it looks like Stata code when the formula calculates (aside from the carets), and copy the formula in column D down to the end of your list. Then copy the whole block of Stata code in column D generated by the formulas into your do-file, and do a find and replace (be careful here if you are using the caret elsewhere for mathematical uses!!) for all ^ to be replaced with ", which will end up generating proper Stata syntax.
(This is truly a brute force way of doing this, and is less dynamic in the case that there are subsequent changes to your generation list. All--apologies in advance for answering a question here advocating use of Excel :) )