as salam alykom Ibn
As for the 1000 years point mentioned in Suratul Haj, Allah. In this Ayah Allah Is comparing the time we need to do and accomplish things, anything, with His. For us we need to go through multifaceted processes to achieve anything, we also need capabilities and skills which we gain over time. Achieving of taks requires stages and procedures that consume time of course. While for Allah, the whole issue revolves around His Will of Saying be and it is be, therefore in anology when we need 1000 days to achieve things to Allah it is done in only one day.
As for the same meaning mentioned in Ayah 4 of Surat Marej saying:The angels and the Rûh [Jibrîl (Gabriel)] ascend to Him in a Day the measure whereof is fifty thousand years". Here Allah S&T Is describing how long would be the Day of Judgment to the non believers who are out of deep fear would be feeling the day although it is just one day as it was 50 thousand years. May Allah recuse us and conceal us on that Day.
Another very good example of abrogation is the Ayahs of:
<b>"O you who believe! Fear Allah (by doing all that He has ordered and by abstaining from all that He has forbidden) as He should be feared. [Obey Him, be thankful to Him, and remember Him always]," (Quran 3:102)
</b>
when this Ayah was revealed, it became very hard on the companions who spent night standing up praying. If u think about it, it is almost impossbile that we fear Allah the way He should be feared.
Then Allah abrogated it with the Ayah saying:
"<b>So keep your duty to Allah and fear Him as much as you can
</b>;" (Quran 64:16)
Just look at the second one Allah manifested with His Name the Merciful.
Major part of the aborgation is explained through Allah's Wisdom and also Mercy.
For instance this Ayah represents Allah's Mercy. He of course Knew how it would be, but only Wanted to show us how it could be if we were commanded to fear Him the way He deserves to be feared. Then told us fine I know it is hard just do what u can do. It has nothing to do with changing mind no it shows His Wisdom and Mercy.