I am not sure how to express the following situation grammatically. I will explain the situation as much as possible. Please help me with this.

It is necessary to pass the X exam to get admission for the B university.I have passed the X exam in January and applied for the B university in the same month.The university gives its final decision on admission in April to December.The score I obtained in the B exam was sufficient for me to apply for the university.
Nevertheless, I am going to do the exam again in April, because I know, a better score increases my chance of being offered admission. I hope to get a better score and replace the previous score with the new score. But I have no idea whether this is possible or not.
I want to ask whether I can replace the previous score with the new score by the time that I receive results in April.
By the time that I would be getting results in April, there is also a chance that the decision will have been made. In that case I will obviously have no use of the second attempt.
I came up with the following sentences. I feel the first sentence and the last sentence are better. Could you please help

Am I allowed to replace my previous X score with the new X score, if a decision on my application
have not been made by that time?
Am I allowed to replace my previous X score with the new X score, if a decision on my application
had not been made by that time?
Am I allowed to replace my previous X score with the new X score, if a decision on my application
will not have been made by that time?
Am I allowed to replace my previous X score with the new X score, if a decision on my application
would not have been made by that time?
Am I allowed to replace my previous X score with the new X score, if a decision on my application
is yet to be made by that time?
Please suggest me new sentences , if all of the above sentences are not good.
Thank you very much.
