...it would be a great improvement were the star to provide a screen-wide comment box."
"would be" introduces a conditional clause, which in full, is:
"...it would be a great improvement if the Star were to provide a screen-wide comment box."
"were" is used because the writer considers it very unlikely that his recommendation for the improvement will eventuate.
In writing such conditional sentences, we can place the verb first, and then omit the 'if', as in your actual sentence.
does "were ... to provide" mean the same as "if ... had to provide"?
No. If the writer wrote
"...it would be a great improvement if the Star had to provide a screen-wide comment box."
then the writer is suggesting that some pressure should be brought to bear upon the software writers/publishers of this software to make them include a 'screen-wide comment box.'
following the same line, can I say "I am to buy new locks for this door" mean the same as "I have to buy..."?
Understanding the meaning of 'am to' depends on the context and tone of voice of the speaker. For example, I remember a movie (?"From the Terrace") in which a woman is in bed, on the phone, and talking to her husband who is out of town. The husband is warning his wife about a particular man whom he doesn't trust, and says that he doesn't want her to socialize with him any more if she runs into him at parties etc. She tells her husband OK. She hangs up, rolls over, and the camera now shows us that the man the husband was warning her about is actually in her bed, 'spending the night', and obviously, this has been going on for some time! The wife says to him: "I'm/I am not to see you any more." Here, she is repeating the husband's order, but it is also obvious from the smile on her face that she has no intention of taking any notice.
An employee who has been before a disciplinary hearing about lateness for work, or some other misconduct, might come out of the meeting and tell those waiting to hear of the result, "I'm not to be late any more or it's the sack. No more warnings." Here, his sombre look and serious tone of voice would indicate that he will probably try hard to correct his behaviour. In using "am to" the speaker is objectively reporting something which he has been told to do.
"Have to' includes the idea of force, pressure that has been placed on the speaker, as in "The judge says I have to repay the money I stole."
'must' indicates greater insistence. But there are previous threads which address the particular differences between these two.
Student or Learner